I've updated all of my computers here to SP3 with no issues. They have been updated by the automatic option and also manual. It has to be a hardware problem. I would start with the video card. Borrow a cheap one from a friend and install it in your computer and try booting. If that works then you know it is your video card. Start removing other expansion cards one by one if this doesn't work. Then start doing the same thing with CD-ROMs extra hard drives, and finally RAM chips.