you need a disc that says vista on it put it in and will give an option to repair or install a new version click on repair first if no joy and you dont have anything of importance on pc pics n stuff then do a new install
good job im only 33 thenbit to go yet lol must be a virus of some sort it started last night ive run scans but still same when you are reading posts some of the words are underlined thats where they are the ads for phones and shopping that is lol