Windows XP hangs up when boot up and shut down

It seems that I also have a problem with shutting down and rebooting my window xp sp3. Every time I shut down my pc, it just hsngs on. No message is given. The power is on and I can move the pointer but cannot shut it with the Ctrl+Alt+Delete. it will stay on till till I turn it off from the power button. The same thing happens if I try to restart it from the shut down menu. I have tried many things but nothing works. It's really frustrating.
I don't want to format my pc for such a problem but I might do it if I didn't find a solution soon.
Please help me if u can!!!!!!
By the way, I have just formatted my pc and haven't installed any programmes other than the drivers. So there are no programmes installed yet and i don't want to go ahead with this, in case I have to reformat it.
Please help...... I'm tired of trying solutions.
Thanks