windows 2000 pro shutdown?

I have a asus k7 motherboard, amd 750 processor,SB live soundcard, 3dfx 16mb video card, 2 operating systems(win 98, 2000) on a 30 GB 7200 rpm hard drive. I’ve had this running fine for about a month and now it won’t shutdown or restart in win 2000?Can anyone help?