Ok, so.

My motherboard fried a few months ago. So I took my old hdd out of the tower and placed it in an older computer (not as slave, but as master - the original owner of the tower kept her hard drive). It recognises the hd fine and even gets to the screen where you have your choice of kernels to boot from, but then it beeps and goes back to the initial startup screen with memory check and whatnot.

Is there a reason why I'm not able to load any operating systems? Is it something I can fix in the BIOS or do I need to redo everything from a Fedora disk?

Motherboard: via tech chipset
hdd: maxtor
Latest kernel: FC2 2.6.10 (haven't brought it out in a while, see)

If the drive containing Linux used to be a slave but now it's a master, the problem is probably just that your bootloader (eg, lilo or GRUB) is expecting the root partition to still be in its original location (eg, /dev/hdb) when it actually is now in a different location (eg, /dev/hda). As a result, when it boots it cannot find what it's expecting.

To fix it, you just need to edit the bootloader file, which may require that you use a Live CD such as Knoppix so that you can get Linux running, then edit the file using your preferred editor. Save your changes, remove Knoppix, and if all goes well you'll be back in business. Also, make sure that your drive is jumpered correctly

The linux hd was the master on the previous computer and the root partition was in /dev/hda. Would it be possible that the bootloader (GRUB in my case) in ANY circumstance could have been confused anyway? (I'm getting a bootable CD in the meantime to try and locate the error, but it should be easier than this to switch a hd into a different computer.)

Edit: just to make sure, I rechecked the cables and all is properly connected. There's just this neverending loop of memory check screen - kernel option screen - tiny blip of something at the top - memory check screen. It looks like it's trying to do something, but is not successful so it reverts back to the startup screen.