Failed Boot

I tweaked my registry, but prior to tweaking I backed up the registry to a second hard drive using the backup utility of windows xp pro. After completing the tweaking I attempted to reboot. Reboot failed, I tried safe mode reboot, again it failed, I attempted, every option in the F-8 menu failed. The boot goes so far, stops and then starts the boot process again, and again and again. I can get the computer to a dos prompt using the XP instalation disk. Ay suggestions short of reinstalling windows XP. I could use information on restoring the registry back up without XP running. Any help would be appreciated.

Have you overclocked your comp.. or do you use Xteq tweaking app'…?

I used a pcmag utility called registryrobot and it seemed to work well until the reboot