If Task Manager is disabled by virus, please try this steps

Click on start, click run or press Windows key and R simultaneously on you keyboard and paste this code ad hit enter key on your keyboad

reg add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableTaskMgr /t REG_DWORD /d 00000000 /f | reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Group Policy Objects\LocalUser\Software\Microsoft\Windows\CurrentVersion\Policies\System" /v DisableTaskMgr /t REG_DWORD /d 00000000 /f | reg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system\ /v DisableTaskMgr /t REG_DWORD /d 00000000 /f | reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon" /v DisableCAD /t REG_DWORD /d 00000000 /f