When ever I press alt+ctrl+del an error message pops up tat administrator disabled task manager... tis problem came after I installed new copy of windows xp...

It seems that you are logged into the PC as a "guest" or a limited access user. Is this your home computer? Did you enter an administrator password during install?

Logoff, then login again using the Administrator account. User name will be Administrator, and the password will be whatever you set during the installation.

Check control panel and under "user accounts" change your user access to administrator.