I suggest you do the following:
right click on my computer-Properties
there click on advanced-startup and recovery
disable automatic reboot
the next time you try to shut down your computer you will probably get an error message about nv_agp.sys. This is some kind of a driver conflict with Nforce2 mobos and PCI display cards, I had the same problem and the error went away when i deleted the file. However, you will need the file if you install a AGP card in the future.