ubuntu can't boot on start up

please somebody I really need an answer

Did you install Ubuntu with this external hard drive connected ?
Did you boot successfully one time with external hard drive unconnected since installation ?
Perhaps the Master Boot Record is on external hard drive.

You could also running following procedure to gather more data:
----------------
There is a standard script provided to analyse boot configuration. Could you download script at:

   http://sourceforge.net/projects/bootinfoscript/

Then in a terminal (Ctrl+Alt+T) run command:

    sudo bash ./boot_info_script055.sh

This will produce a file named: RESULTS.txt. Paste content of this file in http://paste.ubuntu.com/ and provide in this thread the link to Web page. Please don't post file directly in thread, else it will make thread difficult to read.

nope I have ubuntu for at least 2 months now and it was installed using my flash drive not my external hard drive, and it's been great, yesterday I shutdown my cp and then I booted up this morning I realise that dang it's going to try to boot from the external hard drive that is still installed and so while it was booting I pulled the usb out, i thought it would begin to boot normally but it kept giving me an error dev/sda1 no such directory pretty much os isn't mounted I tried to cut it off and back on same thing how do I change this , and I couldn't run what you ask because apparently when running ubuntu using a live usb I don't have certain permissions to run certain things

I have no idea of what happened. One solution to try is to reinstall Grub2 (boot loader) from Ubuntu flash drive: https://help.ubuntu.com/community/Grub2#Reinstalling%20from%20LiveCD
About permissions, you should have all permissions with Live CD.

don't know why but it's telling me I don't have read/write access or that I need to be root, It really can't be that big it seems that somehow things have switched because the OS used to be mounted on sda1 now it's sdb1 which is where the flash drive partition usually was but some how things are reverse and it won't boot I'm getting the grub I can choose to boot it, or recover or check memory but the boot options give me error because the partition that the OS is on want mount there's no way to edit this to fix this issue if I was to reinstall the whole OS is there away to keep my files such as movies pictures ebooks etc

Could you use some punctuation ? English is not my native language and you are not making things easier !
You have to boot from Ubuntu USB key and choose "Try" instead of "Install". In a live session, you can run "sudo" command without providing password, and so you can run the commands provided in https://help.ubuntu.com/community/Grub2#Reinstalling%20from%20LiveCD
When you have many external devices the order is undefined, so letters of "sd#" names can be switched. So don't try to reinstall Grub2 with external drive connected. If you only have one internal drive and an external USB key, sda should be internal disk and sdb external USB key. To avoid such issue, Grub2 doesn't use "sd#" names but UUID of disks and partitions, which are independent of enumeration order.

okay I've been running Ubuntu using a USB since this morning so that step is unnecessary, and I haven't connected my external hard drive since I unconnected it this morning, I've been doing some sudo commands but it's been telling me I don't have permission because I need read write access or I need to be root,

ubuntu@ubuntu:~$ fsck /dev/sdb1
fsck from util-linux-ng 2.17.2
e2fsck 1.41.12 (17-May-2010)
fsck.ext2: Permission denied while trying to open /dev/sdb1
You must have r/w access to the filesystem or be root

following the steps of the link that you provided I get this result:

ubuntu@ubuntu:~$ fsck /dev/sdb1
fsck from util-linux-ng 2.17.2
e2fsck 1.41.12 (17-May-2010)
fsck.ext2: Permission denied while trying to open /dev/sdb1
You must have r/w access to the filesystem or be root
ubuntu@ubuntu:~$ sudo fdisk -l

Disk /dev/sda: 2003 MB, 2003795968 bytes
255 heads, 63 sectors/track, 243 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

   Device Boot Start End Blocks Id System
/dev/sda1 * 1 244 1956736 b W95 FAT32
Partition 1 has different physical/logical endings:
     phys=(242, 254, 63) logical=(243, 155, 40)

Disk /dev/sdb: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0008084f

   Device Boot Start End Blocks Id System
/dev/sdb1 * 1 19076 153219072 83 Linux
/dev/sdb2 19076 19458 3068929 5 Extended
/dev/sdb5 19076 19458 3068928 82 Linux swap / Solaris
ubuntu@ubuntu:~$ sudo mount /dev/sdXY /mnt
mount: special device /dev/sdXY does not exist

just more info

ubuntu@ubuntu:~$ sudo fsck /dev/sdb1
fsck from util-linux-ng 2.17.2
e2fsck 1.41.12 (17-May-2010)
fsck.ext4: Device or resource busy while trying to open /dev/sdb1
Filesystem mounted or opened exclusively by another program?

just more info:

saying the file system can't mount because DBus error org.gtk.Private.RemoteVolumeMonitor.Failed: An operation is already pending

keeps saying that the file system is busy any suggestions

anybody have any suggestions on why It won't let me just do a clean install, I got frustrated in just said forget it, it will probably be easier just to do a clean install plus the majority of my files are backed up, but when trying this it got to the step of formatting partitions and never progressed from their so much so that it didn't do any formatting at all so then I went back to trying to figure out the solution to the original issue which is figuring out how to get Ubuntu 10.10 to boot normally so I don't have to keep using the live usb to work on the PC

If you have a backup of all data, boot on Live session, and with Gparted erase DOS partition table (not partitions, but partition table) and make a new one. If you succeed, you will be able to install on whole disk.

exactly how do I do that do I just go to create new partition table which erases the hard disk

don't know how exactly do I delete the dos partition table

never mind I'm good to go thanks man I really appreciate your help