XP Pro will not Logoff, Restart or Shutdown. Unrespsonsive

I have a new Dell laptop that has decided to be completly unresponsive when requested to Logoff, Restart or Shutdown. The only way to power down is to hold in the power button. Performed a virus scan and came up with nothing. Have turned off USB Root power manangment, no help. Have restored system to prior point, no good. Any other suggestions?