Start button does not work

Windows Vista Home Premium.
Suddenly start button does not work. Right click on start button does work. Mouse is fine, left clicks on anything else. If I do right click and select properties and "customize" start menu and choose "use default settings", no help. But if I select "classic start menu", it works and I can left click on the start button to do what the start button is supposed to do.
Restarting doesn't work. Restored to 2 days ago (though problem started this afternoon) without benefit. Nothing here, or at Microsoft help. Other interesting thing is that some programs have check boxes blacked in, can't be checked. Ran McAfee, Spyware Doctor, Spybot.
Now that the "classic start button" thing works, I'm more concerned about the blacked out check boxes! All thoughts appreciated.---David