Fixing an overclocking boo-boo?

I built a computer for a friend a few years ago...
Celeron 533MHz (Overclocked to 544, OOOHHH!)
128Mb Ram, 12Gb Primary Master 5400rpm HD, 15Gb Primary Slave 5400rpm HD, 50x generic CDROM, HP 9500 CDR/RW, 1.44Mb Floppy.  
Recently upgraded to WinXP Home.    
Not that any of that may be particularly important to the question which is as follows...
Same friend calls me recently to say he wanted more power but thinks he OVER overclocked it in his ill-educated attempt for more power.  My original settings were 8X multiplier and 68MHz CPU core clock.  He said he turned up the CPU clock and said that it completed POST saying 644 or 664MHz but after finding all the hardware, the computer simply locked, with the HD indicator stuck on.  When I tried to turn it on, it completed POST and then gave a message stating that it needed a startup disk to continue.  I powered it down in order to restart and work in the BIOS to resolve the issue.  I restarted the computer and it never completed POST, no beep or beep code at all, and no on screen message.  I took the computer apart down to the bare minimum just to test POST and still no luck.  This is the state the computer is currently in.  I tested the monitor and it is good, I disassembled and reasseembled the WHOLE computer and tested most of the parts to be good and the results are still the same.

Is it a simple case of CPU burnout?  Maybe a bad power supply?  Why did it POST a few times and then just stop?


Let me know, and thanks in advance!

Josh Wardell