Running windows XP SP2 I can be waiting for up to 5 minutes after hitting the shut-down button until the machine actually switches off.

I have tried killing an non essential services/application before I shut down to see if that makes a difference but it doesn't appear to.

Can anyone suggest why the machine takes so long to close down and possible solutions (NOTE: To actually boot up the computer is extremely quick and I don't have many application/services starting up either)