To re-enable the Task manager, do this:-
Step 1:In the Start>Run box, type gpedit.msc and press enter. This will open the Group Policy editor.
Step 2:Navigate to User Configuration>Administrative Templates>System>Ctrl+Alt+Del options using the left side pane.
Step 3: Double click on "Remove task manager" entry in the main area.
Step 4:Click on the "enabled" radio button and apply the changes.
Step 5:Reboot!
If this doesn't work or if Group Policy Editor is not present, Enter this in the run box(Start>Run):-
Code:
REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableTaskMgr /t REG_DWORD /d 0 /f
This ought to do it!
Also, if you plan on running HijackThis, as suggested by Varad Dilip Choudhary,
NEVER remove all that it shows! Save the log file and post it here for analysis.