I fixed my black screen problem by realising that the bios boot section had moved my usb drive to the main boot drive. the only way to get around this is to disconnect all usb devices (leave keyboard attached) boot the comp 1 - 5 secs go into your bios make sure that the main boot device is the hard drive with windows on it, save and boot again and it should load windows (7) in my case, if not then boot and 1 - 5secs in press F8 and manually choose your hard drive to boot from, I realise that differnt motherboards have different keys to press, but they all should allow you to choose which hard drive to boot from manually. After you get into windows create a back up and then fix the comp with windows repair and it should successfully rewrite the boot commands again. I hope this helps.