OS keeps crashing at random intervals

I thought I knew my way around a PC, but this case is driving me absolutely insane. Help.
Basically, the system runs fine for a few days or weeks, then the OS just dies. Error message: "Reboot and select proper boot device."
Originally, there was a 250GB SATA drive in here, but it finally bit the dust after a few years (confirmed dead; tested it in another machine). I swapped in a 120GB PATA drive with Windows XP 32-bit, and it worked for about a year or two. When XP crashed, I reinstalled it and it held up for a few months. Now, the crashes are getting more frequent. Once the install on the 120GB drive wouldn't even complete, I grabbed a used 80GB PATA drive (which works perfectly in another computer), threw Windows XP on it, and it crashed within a week. Tried Windows 7? Crashed in a couple of days. Swapped out the power supply and the RAM—still nothing. I'm losing my mind.
The crash happens upon rebooting, not while actually using it.
Drives are connected correctly: master-slave configuration.
Now, installing XP won't even start because it claims the 80GB drive is "damaged."
I noticed something weird in the BIOS: when it tries to read the drives, the descriptions sometimes look like gibberish.
For example, instead of ST120E11, it shows !!T120E11. Or for the 80GB WD80..., it shows !“*WD80...
Sometimes it reads them fine, but then the error comes back.
I pulled the CMOS battery for a minute to reset the BIOS, reinstalled the OS, and it worked again—for exactly one day.
Is the motherboard shot? It’s hard to believe both drives failed at once.
I know what you're going to say—it's an old piece of junk—but has anyone dealt with something like this before? What's the culprit?
Specs (circa 2007/08):
Drives (PATA): 120GB, 80GB
Motherboard: Asus M2N-MX
CPU: AMD Athlon XP 64
RAM: 2x512MB 800Mhz DDR2

If you can, hop into Windows right now and download CrystalDiskInfo... Once you've got it installed, it'll show you exactly how everything is holding up.

A blue status means your drives are looking good—everything is running smoothly.

Yellow means things aren't quite right with one of your disks; the program will give you a heads-up on what's going on.

Red is the warning sign—it means you've got a serious issue on your hands. If you see that, you should probably start backing up your important files immediately and start thinking about picking up a new drive.

Larry Ortiz5 said:If you can, hop into Windows right now and download CrystalDiskInfo... Once you've got it installed, it'll show you exactly how everything is holding up.

A blue status means your drives are looking good—everything is running smoothly.

Yellow means things aren't quite right with one of your disks; the program will give you a heads-up on what's going on.

Red is the warning sign—it means you've got a serious issue on your hands. If you see that, you should probably start backing up your important files immediately and start thinking about picking up a new drive.

Thanks,
I wiped both drives, managed to get Windows XP 32-bit and CrystalDiskInfo running, and they're both showing blue. Everything looks fine for now.😕, we'll see how long they actually last. Cheers.

It could potentially be a motherboard issue—it’s always a possibility. You see, those electrolytic capacitors can be real troublemakers, and they often manifest themselves exactly the way you described. I'd suggest taking a close look to see if any of the capacitors on the board look swollen or bulged out—though, mind you, they can still be completely shot even if they look perfectly fine to the naked eye.