First off, I should say that the computer that's having problems is not mine, but my mother's.
Okay, the computer is a Compaq Presario R3000 Laptop. Uh . . . I don't know much about it. I know that it has an AMD Athlon XP-M Mobile processor, but I don't remember how fast. It was under 1Ghz, I know that much. It's got an estimated 250MB of RAM, it's running Windows XP, and it's about 2 years old. All that information is what I remember from when I last looked at it, and that's also all I can find out.
I was not there when the problems started happening, but according to my mother, the hard drive started "grinding" and the computer began to slow down to an almost unusable speed. She told me that she tried to run Disk Defragmenter, Disk Cleanup, and Norton Antivirus at the same time, and when she did, she got the Blue Screen of Death, and then the computer shut down instantly. She tried to get it to boot up a few times, but it would never get past the Windows XP Start-up screen.
When I woke up this morning, she told me what had happened, and I tried to fix it. I immediately noticed that the hard drive was humming particularly loud, and that the hard drive light was on permanently. It did ehe same thing for me as it did for my mom, but I let it sit a while and it eventually got to the log-in screen. However, it was running extremely slow. It took half an hour to get to the desktop, and then it took another half hour to load the icons, taskbar, and clock. It took another twenty minutes to bring up the power status thing next to the clock. That's when I tried to open "My Documents", which it never did. I shut it down because it stopped responding, and now the screen won't even turn on.
I know a lot about computers. I've fixed computers that have crashed before. But I can't figure this out, no matter what I think of. Can anyone help me with this?

Sounds like your hard drive has crashed, and will need to be replaced.