Xp auto log off after login.

Hello,
My Name is Swetank and i have two operating system on same pc. First one is Xp and other One is Windows 7. Few days ago suddenly on a virus scan i found many viruses may be a malware which is not stopping to clean or delete. It was fairly very night so i stopped the scan and thought it to do next morning. Next morning i was unable to login. As i entered my password it displays the wallpaper for few sec and log off automatically and again the same situation came back.

I used my another os to make it all right but nothing happened!

Please help me to solve this problem.
Thank You!