Reinstalled XP and now it restarts when i click turn off

[charltonfan1]

Never had this problem with my previous installation of XP, but ever since i reformatted my GF's when i ask it to Turn off in the start menu it will say its shutting down, the monitor goes into standby but then the PC powers up again. This only happens sometimes, the other times it shuts down fine and i'm not doing anything different each time.

Any ideas?