how to enable the Task Manager disabled by virus

Click Start
Click Run
Enter gpedit.msc in the Open box and click OK
In the Group Policy settings window
Select User Configuration
Select Administrative Templates
Select System
Select Ctrl+Alt+Delete options
Select Remove Task Manager
Double-click the Remove Task Manager option
And as I mentioned above, since the policy is Remove Task Manager, by disabling the policy, you are enabling the Task Manager
or
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Click Start -> Run. Type in "regedit" (no quotes) and hit Enter.

Search for HKEY_CURRENT_USER -> Software \ Microsoft \ Windows \ CurrentVersion \ Policies \ System.

Look for: DisableTaskMgr. Click on REG_DWORD. Value: 1=Enable this key (disables TaskManager); Value: 0=Disable (actually enables TaskManager)

Close RegEdit