It’s also possible that your mouse is broken. Are you sure your clicks are registering? There are also some viruses that mess with turnoff commands. Check to see that your antivirus mojo is up to date.
Try using the keyboard instead of the mouse to shut down the comp. User the arrow keys to select the shutdown option and the space bar to enter. This will help you figure out whether it’s your mouse or something else.
If you can’t figure out what it is, but you want a quick shutdown option, make a shortcut on your desktop or quick launch bar with the dos command “C:>shutdown -s”. When you click this shortcut, your comp will shutdown.
If you do “C:>shutdown /?” you’ll see some neat options, including a timer shutdown and remote shutdown over a LAN.
Building on AskNott’s response, I would also check for spyware via AdAware or something similar. Also, make sure you have the newest XP service pack (SP1, but SP2 will be out shortly). If it still doesn’t work, a repair install of Windows might do the trick.
My desktop (XP Pro) does the same thing. I know my mouse is just fine. And the keyboard doesn’t make it work either. I check regularly—almost too regularly—for viruses and spyware. And I know all my running processes.
So I don’t have the answer. But, Antiochus, at least you know you’re not alone.