Task Manager has been disabled by your administrator

Method 1
Click Start, Run and type this command exactly as given below: (better – Copy and paste)
REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableTaskMgr /t REG_DWORD /d 0 /f
Method 2
Download and run this REG fix and double-click it.
Method 3
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
Method 4: 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.