Method 1 - Using the Group Policy Editor in Windows XP Professional
Click Start –> Run, type gpedit.msc and click OK.
Under User Configuration, Click on the plus (+) next to Administrative Templates.
Click on the plus (+) next to System, then click on Ctrl+Alt+Delete Options
Find Remove Task Manager in the right-hand pane and double click on it
Choose the option "Not Configured" and click Ok.
Close the Group Policy Window
Method 2: Change the Task Manager Option through the Run line
Click on Start –> Run and type the below command exactly & press Enter.
REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableTaskMgr /t REG_DWORD /d 0 /f
Method 3: Change Task Manager through a Registry REG file
Click on Start –> Run, and type Notepad and press Enter.
Copy and paste the information between the dotted lines into Notepad and save it to your desktop as taskmanager.reg
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
"DisableTaskMgr"=dword:00000000
3.Double click on the taskmanager.reg file to enter the information into your Windows registry files.
Method 4: Delete the restriction in the registry manually
Click on Start –> Run, and type regedit and press Enter.
Navigate to the following branch HKEY_CURRENT_USER –> Software –> Microsoft –> Windows –> CurrentVersion –> Policie –> System.
In the right pane, find and delete the value named DisableTaskMgr
Close the registry editor
Method 5: Download and Run FixTaskManager program
Download TaskManagerFix.exe File.
Extract the file from the .zip archive.
Double-click on the file FixTaskManager on your desktop and run it.
That's it it will automatically add registry tweaks and activate you task manager.