Hi,
I'm not able to open the task manager. It appears for a second and then disappears when I press ctrl+alt+del or when I click on task manager from the task bar. What can be the problem? I use Windows XP professional.

The Task Manager exe file might be corrupted. If you have a Windows XP CD, you could try replacing your current task manager with a fresh one.

To do this, put your XP cd in the drive, and open a new command prompt (Start > All Programs > Accessories > Command Prompt).
Type D: (if D is the letter of your drive), then type
"cd i386" (without quotes),
Then type
"expand taskmgr.ex_ C:\WINDOWS\system32\taskmgr.exe" (again, without quotes)

Close command prompt, restart your computer, and try Task Manager again. If that doesn't work, you could try a repair install of XP.

This error is caused if the DisableTaskMgr restriction is enabled. To enable Task Manager, try one of these methods:
METHOD 1
Click Start, Run and type this command exactly as given below: (better - Copy and paste)

REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Pol icies\System /v DisableTaskMgr /t REG_DWORD /d 0 /f

Method 2
Download and run this REG fix and double-click it.

Method 3
Click Start, Run and type Regedit.exe
Navigate to the following branch:
HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Policies\ System

In the right-pane, delete the value named DisableTaskMgr
Close Regedit.exe

Method 4: Using Group Policy Editor - for Windows XP Professional
Click Start, Run, type gpedit.msc and click OK.
Navigate to this branch:
User Configuration / Administrative Templates / System / Ctrl+Alt+Delete Options / Remove Task Manager

Double-click the Remove Task Manager option.
Set the policy to Not Configured.