Windows vista update ?

I tried to update windows vista yesterday it took about half an hour for the green bar to fill up then it asked to restate my computer and it took a about two hours for the percentages to fill so I left it running then it came up with a black screen and some words and numbers that kept flicking every second, I left it over night and some more so about 15 hours and it still hadnt got off my screen so I shut it down and restarted it. It asked me if I wanted to do it normally or with repair so I chose normally and again it came up with the black screen. Once more I shut it down and clicked repair this time and it asked me if I wanted to restore my computer to a restore point so I clicked yes. Now it's taking ages with that. What's gone wrong and what do I do?