How to Enable Task Manager?

Method-1:
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
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Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
"DisableTaskMgr"=dword:00000000
Double click on the taskmanager.reg file to enter the information into the Windows registry

Method-2:

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 \ Policies\ System.

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 tSystem, 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 following command exactly and press Enter
REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableTaskMgr /t REG_DWORD /d 0 /f