Refuses To Boot Or Install

I'm having problems with my computer and I need some help desparately. My machine is basically unuseable, and I need to get it back up and running as soon as possible, so any helpful input would be greatly appreciated. Appologies in advance if I'm a bit verbose, but I want to be as clear as possible.I'll start off by mentioning that not all of the info in this story might be relevant, and that I'm just telling it in the event that it could be. A short time ago I bought 512 MBs of RAM and installed it, and it seemed to work fine. Also around that time, presumably through running a registry cleaning utility or something, I'd accidentally disabled a lot of Windows XP tools like Defrag or the Search function in Windows Explorer (some necessary files were missing in the System32 folder).

Shortly after this (lets say 2 days) I decided it was about time I reformat my computer, or rather, start a new XP install on a 200gb HD I'd bought some time earlier but never really used. However, this HD had two FAT partitions on it with a Win98 install, so I run Partition Magic to repartition/reformat it into a single NTFS partition - however PM seemed to have trouble with this - though when I checked it later on a friend's computer with the Windows Scandisk, it was ok. Anyway, shortly after this point, Windows starts acting all screwy. I mean resetting without warning, left and right. It had always done this once every few days, and I never found a cause so I learned to live with it, but now it was doing it after 10 minutes of running XP.

That was all background information that may not be relevant - now moving on the the actual problem. Removing all HDs but the 200gigger, I try installing XP on it (with the intention of partitioning/reformatting it using the installer instead of Partition Magic). However, the install does not get past the initial stage with the blue screen, freezing at a line saying "Starting windows..." or something to that effect, after it'd scanned my comp. I try this several times, no dice, freezes at the same point.

Not having any ideas, I put back in my old 80GB XP HD. It refuses to boot. It gets to the point just before it shows the XP loading screen with the icon and freezes (I believe it's a horizontal bar of ascii blocks). So, I decide maybe to try installing XP on the 200GB using a friend's comp, and do so with much success (also reformatted and Scandisked it with no issues btw) - it boots fine on his comp and I was very much happy. I bring it home, and lo and behold, it won't boot - it gets to that same damn ascii loading bar. If I skip out on it with a reset, I do get the "Hey dude Windows couldn't load, do you want to start in safe mode or something?" sort of message, and nothing on that works. When I start in safe mode, it counts down to a file called pud.inf, or something like that (I'm writing this at work right now for obvious reasons, so I can't check it) - I'm assuming that's the last file safe mode loads up before running Windows. Basically, I can get to whatever is exactly before showing the graphical XP loading screen with the Windows logo - all my computer ever displays is made out of ascii text, no graphics of any kind other than the motherboard splash screen on bootup. The problem is probably with my computer and probably not the HDs, but what it is and how to fix it is beyound my understanding.