My windows XP professional sp2 OS, restarts again and again without even showing the user list. how to solve?

for one having two OS on your computer increase the chance of crash due to conflicting command prompt parameters you have to due a very thorough job to get it right. Maybe not having a USER list available was one parameters

gilmour_waters - The operating systems are installed on separate disk partitions so the conflicting command prompt parameters wouldn't exist. The boot loader program presents a list of the available bootable partitions from which the user can choose.

SIVAKUMAR - Not sure if what the exact problem is but I'm guessing you could have a driver or service problem that is causing the computer to panic. I don't recall a good reference but I believe Microsoft changed XP to not go to the traditional Blue Screen Of Death (BSOD) in favor of just rebooting the system. Another possibility would be a virus or some sort of spyware, but given that you say the "users" aren't even presented, I doubt that it will be this. See if you can boot into a safe mode and check to see if the event manager has any details that can help in troubleshooting.

Probably the Boot.ini and Boot Loader have had their references changed. If you have a System restore Setup on XP, then you can get it from the Safe Mode. Otherwise, running XP install CD in repair mode will help

I guess that you have to format your computer because the same problem happned with me to on sp2 a virus got on the pc.better u format your pc