My pc is a dell dimension e520. I have been trying to update my bios via the Dell support centre and when it shuts down the computer to reboot it freezes after saying shutting down, the screen goes black as if it`s about to reboot but then freezes with the power light still on. I left it in this state for over ten minutes but as nothing happened I had to turn off mains supply and restart computer as normal. The computer will shut down properly using either the red button on start menu or the shut down writing on menu.