A task manager is some time disable either by administrator or due to some virus if you want to enable there are different methods..
Method 1: Using Group Policy Editor - for Windows XP Professional
- Click Start, Run, type gpedit.msc and click OK.
- Navigate to this branch:
User Configuration / Administrative Templates / System / Ctrl+Alt+Delete Options / Remove Task Manager
- Double-click the Remove Task Manager option.
- Set the policy to Not Configured.
- Click Start, Run and type Regedit.exe
- Navigate to the following branch:
HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Policies\ System
- In the right-pane, delete the value named DisableTaskMgr
- Close Regedit.exe