XP Pro won't start

This is my sons computer. He was using it a couple of nights ago and it froze. He rebooted it and now when windows XP tries to start the computer reboots. I tried to start it in safe mode but with the same results, the computer reboots. I have a Driver Resource and Diagnostic Tools Disk that came with the computer. I ran the diagnostic program and no errors were found. I have been told that this will test the hardware. Any ideas what I can do? Where should I start?

 

Never mind, I figured it out.

 

Maybe you would like to share how you resolved this, so that other experiencing the same issues can learn from your solution too

 

As it turned out there was a bad sector on the hard drive. I had to go into the recovery console and perform a chkdsk. When it said it found one or more errors I did a chkdsk /r. If you don't have a non=recoverable error, you have a chance dto get the computer working again.