I went out today and left the computer on. When I got back, there was a black screen with white writing at the top: 'Please insert boot media device and press any key' (something like that). I pressed a key and it repeated itself. So I pressed the on/off button on my CPU, and it starts up to the screen where you have to choose 'Start in Safe Mode', 'Start in Command Prompt', 'Use last working settings', 'Start Windows normally'. I choose 'use last working settings', and the Windows logo on the black screen with the blue loading bar under it comes up. Then, the screen goes black like it's restarting and goes back to the screen where you have to select what mode to start the computer in. I choose 'start windows normally' and the same thing happens over and over again. I choose 'safe mode' and some stuff starts typing itself out and the same things happens again. Someone help me please? What might've happened? I've got a Windows XP disc, could I use that to fix it?