Logging Off and Shutdown of computer

I log off but the computer screen seems to acknowledge that command but then just goes back to exactly where I was before I gave it the command. Same with Ctrl Alt delete. If I press ShutDown, it seems to accept the command but returns to same screen. It just wont logoff or shut down.I have set a schedule task to shut down at a designated time but that status says "could not start"

It can happen due to many reasons ..

One is file missing operating system and second for any third party software installation or etc .

XP executes an automatic restart in the event of a system failure. Therefore, more or less anything compromising the operating system during the shutdown process could force this reboot.

you can try the below steps :-

Right-click on My Computer, click Properties, click the Advanced tab. Under “Startup & Recovery,” click Settings. Under “System Failure,” uncheck the box in front of “Automatically restart.”

Or if above tip not work then you can Repair your windows to solve this issue !