When I click alt+ctrl+del to open task manager a message comes service is disable .

Try this...
If u have XP Professional than...

Go to start> run > type gpedit.msc
Once in the Group Policy Editor, expand in turn:

User Configuration
Administrative Templates
System
Ctrl+Alt+Del Options
In the right side u will see remove task manager enabled
Double click on it and make it not configured..
Refresh the computer..

Or u can do this

Click Start, then click Run, type in regedit, and click on OK.

Expand these registry keys in turn:

HKEY_CURRENT_USER
Software
Microsoft
Windows
CurrentVersion
Policies
System

There is a value disable task manager delete that..



If above trick dosent seems working

Then try this

Click Start, then click Run, type in regedit, and click on OK.

Expand these registry keys

HKEY_CURRENT_USER>Software>Microsoft>Windows>CurrentVersion>Policies>System>

And at right side there should be "DisableTaskMgr" right click on it and click delete

You should delete this value


If DisableTaskMgr is not shown at right side then search in whole registry key

Just type ctrl+f and in that paste "DisableTaskMgr" and search for it and if found delete that