Why is Windows XP going in a restart loop?

So my computer is going in a restart loop now. I don't know if I corrupted the hard drive or not, but now when I turn on the computer, a message saying "Windows did not start up successfully" and when I press "Start Windows Normally", the Windows XP splash screen will appear for about 3 seconds, then restarts again. I also tried going into safe mode, but that's even worse. The splash screen won't even appear and the computer will restart. I'm now using a bootable CD (UBCD4WIN) and trying to see if I can use any tools there to fix it, but I don't think that will work.

I tried accessing C: from the boot CD, but it saids "C:/ is corrupted and unreadable", so I think I corrupted C drive somehow. I can't use chkdsk on the CD because it can't find C drive! I'm thinking about using the recovery system that came with the computer. I already tried the Windows Recovery Console, but it can't find C:/, it can only find another drive without my windows installation.

So I'm really lost, and I'm almost out of ideas. The computer was working fine yesterday, and when I turn it on today, it was like this! Please help!