One of my XP computers is constantly rebooting, does not go into safe mode also. I have had this problem several times with other computers and the solution has always been as under :
1) Boot into recovery console and do "chkdsk c: /r"
2) Boot into UBCD4WIN and restore registry.
This has always worked but this time it does not. I am still having same error. When I do chkdsk, I get 4Kb bad sectors. Is it possible that system files are in that sector? How to solve this problem. I can see and read the drive from within UBCD4WIN.