running Ubuntu damaged my computer--help!

Make sure the BIOS settings are ok. Also check the RAM using the ubuntu CD.

Did you MD5 test the ISO you downloaded?

"Is my computer totally fried now?"

No. it's almost certainly not damaged at all.

F2 didn't work, which is to be expected. Try F1. That should work.

Ubuntu did not harm your computer (and given what you have said so far, there is no reason to think your computer is harmed at all), though obviously it was bad that it didn't itself work properly. Your present problem was caused by allowing your battery to discharge completely while the computer was turned on. I've seen that before (with computers running various operating systems). It's not a very serious problem, as it's almost always easily fixed. It has two general causes. It's either a design problem (perhaps the tiny CMOS battery on the motherboard holds insufficient charge to maintain a BIOS configuration when AC and main battery power are not provided for an extended time), or an indication that your specific machine is faulty. If you haven't experienced any other problems with your machine, then I wouldn't worry. (Ubuntu crashing might be a problem with your machine, but it might also be due to a bad .iso download or a bad CD burn or bugs in Ubuntu.) It would be a good idea to check your RAM, and also to investigate the cause of the Ubuntu CD crashing (MD5 test the .iso as actionparsnip says, and also press Spacebar as it boots wen the keyboard and person icons appear at the bottom of the screen, select your language, and select "Check disc for defects").

In the future, you can always turn off your computer by holding down the power button, typically for five seconds. (It will turn off while you're holding it down, so you don't have to worry about knowing how long to hold it down for.) That is the case no matter what operating system you are using, and even if your computer is not booted into any operating system. This is not a "safe" way to turn off your computer (as you have yourself said, you should shut down normally whenever possible), but it is much better than any of the ways of turning it off that involve deliberately cutting power.

Hey, thanks for the responses. As soon as I posted this, I ended up solving the problem. I put the Ubuntu CD back in the computer then hit F10 (Computer Setup) then Ubuntu began loading again and I just clicked on logout of Ubuntu, exited the system, ejected the CD then restarted the computer.

But as an FYI, holding down the power button wasn't working. The computer just wouldn't shut down when I was having the problem earlier. The only way I could get it to shut down was to unplug it and wait for the battery to run out. I think what had caused the problem was that Ubuntu just froze and I couldn't properly log out of Ubuntu. I just forced the computer to quit by unplugging it.

Perhaps I should download an earlier version of Ubuntu since my laptop is an older version? I'm thinking that the latest version of Ubuntu might be too much for my old laptop but an older version of Ubuntu might work better?

Anyway, I've gotten the computer to work with Windows XP again but I'm afraid to use Ubuntu 11.04 This may be a stupid question, but how do I do an MD5 test or check the BIOS settings?

Well, if you tried Ubuntu on a CD, that explain a little thing:

Ubuntu requires a Virtual Memory to work better. Since you run on a CD so expect it to be very slow, and of course it has no space to write the virtual memory, which make it only has your system memory to access (and makes it even slower). However, Ubuntu, like every other OS, writes boot information to BIOS or hard disk (usually hard disk), and this process may 'harm' your computer if you are not properly logged out.

@Benjamin Tan Chun Yung
"Ubuntu requires a Virtual Memory to work better..."

The CD is designed to work OK without being able to swap to disk (and it is also able to automatically mount and use a Linux swap partition that is already present on the disk, though that does not apply in this case). Consider that most people have no swap enabled when they install Ubuntu from the CD, and most installations of Ubuntu from CD are successful! Simply loading and poking around a desktop is substantially less intensive than installing, unless you run many programs at once. If there is very little RAM (memory) in the system, then the CD might not work very well, or might be exceedingly slow, but it should never freeze up completely. Furthermore, that holding down the power button did not turn off the machine is suggestive of hardware problems.

If Mer Mer's laptop has very little physical memory, it's possible that could be related to what has happened here. But I would not recommend installing a fully-fledged Ubuntu system on a machine whose physical memory was insufficient to enable even basic operation of the live CD. An earlier version of Ubuntu, or a lighter-weight flavor of Ubuntu (e.g., Lubuntu), would probably be much more appropriate.

"Ubuntu, like every other OS, writes boot information to BIOS or hard disk (usually hard disk), and this process may 'harm' your computer if you are not properly logged out."

That is false.

No operating system writes boot information to the BIOS. While doing so is theoretically possible, it is not actually done (it would not be very helpful, and it would not substitute for installing a boot loader to the hard disk); neither the Ubuntu live CD nor an installed Ubuntu system (nor Microsoft Windows) will do this.

As for writing boot information to the hard disk, this is only done if you install Ubuntu (or do it yourself manually, which is not something one does by accident). This does not happen if you do not install Ubuntu. When you just try out Ubuntu from the live CD, this does not just happen by itself.

Furthermore, if Ubuntu had been interrupted while writing a boot record on the hard disk, that would not have corrupted the BIOS configuration (which is what prevented Mer Mer's computer from booting initially). Instead, it would probably have corrupted the Master Boot Record, and then Windows would be unbootable. So not only is there no mechanism whereby Ubuntu could have written boot information to the hard disk in this case, there is also no evidence that would suggest this had occurred, even if the situation had been different such that it could plausibly have happened.

If you browse or otherwise access your files on disk from the live CD, it will mount the partition(s) containing them. Once this has happened, it is possible that a systemwide freeze/panic could cause disk corruption (but not of the kind that interferes with the beginning stages of booting--Mer Mer's machine had failed to boot **before the hard disk was initially accessed**). In such a case, the corruption would usually be minimal and easily fixed. It would not resemble anything that has happened here.

Disk damage is also theoretically possible from abruptly cutting power to the hard drive if it is being accessed. Practically speaking, without browsing through its contents, performing a test on it, or installing Ubuntu, this would only be a risk (and still an extraordinarily minuscule one) if Ubuntu had detected and automatically mounted a Linux swap partition on the hard disk. Since the only installed operating system is Windows XP and (I presume) no other Linux-based OS has been installed, this does not apply.

@Mer Mer
"But as an FYI, holding down the power button wasn't working."

That is strange (not unheard of, but strange), and worth looking into.

"The only way I could get it to shut down was to unplug it and wait for the battery to run out."

I once spilled tea on a laptop and wanted to shut it off as quickly as possible after unplugging it from AC power. Holding down the power button did not turn it off (this is the only time I have had that problem, and I have not had it subsequently on that laptop, which was fortunately undamaged). I flipped it over and removed the main battery. That did the trick.

Removing the battery is not, generally speaking, any better for your computer than allowing it to discharge fully. But it is certainly much faster. (And when the computer is frozen, it may not be any worse, as the normal process whereby the computer is shut off cleanly when the battery gets too low might not occur.)

"I'm thinking that the latest version of Ubuntu might be too much for my old laptop"

Depending on how old your laptop is, that might be the case, but it should still not have frozen up.

What is the make and model of your laptop?

"how do I do an MD5 test or check the BIOS settings?"

You can enter your BIOS setup by pressing F10 when prompted to do so, while your computer starts up. (This is not the case for all computers; different computers have different keys for entering the BIOS setup.) Then you can look through the settings and make sure they look OK. You might or might not have the ability to discern whether or not they are correct, so you may want to ask someone you know, who is knowledgeable about computer hardware, to take a look at them. Or you can post about them here. However, since your computer is starting up again, this is not a high priority.

(It is still the first thing I would do, if it were my computer, but if it is very difficult for you to determine if your BIOS settings are correct, then it may not be worth the time and effort. It does occur to me, however, that the documentation that came with your computer may tell you what the different BIOS settings mean and how to determine if they are set correctly. If your computer is old, it is perhaps more likely to have come with more thorough print documentation than many new computers these days.)

I do definitely recommend:
(1) MD5 testing the .iso image.
(2) Checking the burned disc for defects.
(3) Testing your memory.

The natural order to do those things would be 3, 1, 2. But since the easiest way for you to test your memory is by booting from the Ubuntu CD and selecting that option, I recommend doing it in the above order.

To MD5 test the CD, follow the instructions at https://help.ubuntu.com/community/HowToMD5SUM. If the MD5 sum does not check out, then you should download a new Ubuntu .iso image, and burn a new CD from it (after MD5 testing the new .iso image).

To check the burned disc for defects, boot from it, press Spacebar when the keyboard and person icons appear at the bottom of the screen, select your language, then select "Check disc for defects". If it does not check out, then either there is something wrong with your computer (typically either the RAM or the CD drive), or there is something wrong with the burned CD. Most of the time, it is the latter. So burn a new CD, make sure to do it slowly (select the slowest available burn speed), and make sure you are burning it correctly according to the "Show me how" instructions in Step 2 of http://www.ubuntu.com/download/ubuntu/download.

After the CD is verified as good (or it fails verification and you burn a new CD which passes verification), then check your RAM (memory) by selecting the option for that in the same menu from which you had selected "Check disc for defects" before.