I am running windows xp on a Dell Optiplex GX280. This is the original windows that came with the computer. For some reason the computer started rebooting on its own for no reason and it has only gotten worse. Now it will freeze up and nothing will help short of a hard shut down. Does anyone know what might be causing this? I have run anti-virus and anti=-malware checks but they all come up with nothing. I am at my wits end.