When ever I turn on my Mac there is always a '4' on the App Store icon. Going to the store and hitting 'Update All' shows a progress bar. Quitting App Store and leaving, the same '4' updates show up again, in a perpetual circle.
If your system is NOT managed, odds are it's a corrupted / stale update cache. This is an amazingly common problem on OS X, and I'm stumped as to why Apple doesn't make it easier to fix. Anyway, go into ~/Library/Caches and find files called com.apple.appstore and com.apple.softwareupdate. Delete them. Log out and back in (just to be safe). Try again - should work now.