Windows Vista Start button not working?

Yes I have a Validated copy of Vista. It came pre installed on my machine. It worked just fine earlier today... then after a few hours I clicked it and nothing. This has never happened before. I tried the start menu button on the keyboard and that worked once but not since. I've googled the answer for this fix but I don't really understand it... Can anyone dumb it down for me? I'd really hate to have to do a system restore when I can't back up my system... Is there another way to fix this?