Moved to 10.4 but want to move back to 9.10?

You musty reinstall Karmic, you cannot downgrade

I have the Ubuntu 9.04 CD but when I put it in my computer nothing happens. I inserted the disc & restarted my computer, and nothing.

you need to tell your PC to boot from the CD. Make sure your backups are recent in case of catastrophe. If you have a seperate partition for /home then you are smug and can simply set the system partition for formatting, if not you will need to format fully and reinstall from clean.

Okay, how do I do that? I've been with Ubuntu for awhile but not very familiar with all these technological computer stuff.

When I put the 9.04 CD in the computer I see a icon on My Desktop it says Ubuntu 9.4 i386. I also go to system, administration, Start Up Disk Creator and make sure it's on the start up disk but when I restart it still nothing happens.

You won't see it on any desktop. You need to tell the PC to boot the CD before the current OS even loads. You only need the usb-creator app if you plan to install via usb but the system has an optical drive so is not reuired

Thanks actionparsnip, that solved my question.

Thank You for your help I was able to install Ubuntu 9.4 back on my desktop.