If TaskManger has been Disabled it can be due to various reasons,due to Viruses,Malware and Spywares also,Take a look how to solve this Probelm which Involves two Solutios.tma
Sol1:By applying windows Group Policy Editor

  • Click Start button click Run and Type Gpedit.msc Navigate to User Configuration\Administrative Templates\System\Ctrl+Alt+Del Options\Remove Task Manger
  • Double Click Remove Task Manager and set it to Not Configured

Sol2:By Using Registry Editor

  • Star Run and Type Regedit and Click o.k
  • Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows current Version\Policies\System
  • In the Right pane delete Value DisableTask mgr
  • Close Registry Editor.

Note: Regediting is Dangerous be Sure to make a Backup of your Registry