I'm running XP Pro. It starts to load, gets to the users page (sometimes), shuts down and starts all over. This continues until the PC is shut down. Once, it actually made it all the way through and worked for a short time, although the screen icons were "not as usual". Since then it has only made it to the Windows screen with the moving blue bars and then shuts down and restarts the process all over.
I removed the HD and reinstalled it in a different PC. I was able to read the files, but it still wouldn't boot. I have tried a couple of virus removal programs and they all report no infections. I tried a repair of XP per your instructions, but that did not resolve the problem.
I purchased a new HD thinking that would surely resolve the problem...it didn't. Now the new HD has the same problem, except that when I tried to install it in a different PC as a slave drive it wouldn't let the master drive boot either.