RE: XPS 8500 will not start, orange light on motherboard, will not boot, BIOS inaccessible, black screen
Disconnect the Hard Drive Data cable and see if it will POST with bad hard drive message. You could also try the BIST button. Before you can tell what is wrong you have to be able to determine what is ok. You don't want to remove the hard drive power cable because this is a load that should always be there. A bad power supply may also be the issue.