Startup Error

As soon as GMod starts up, about five seconds later it crashes, with an error saying “NO STEAM APPS”. This is when the background comes up, but before the cyan loading bar appears. It just started happening a few seconds ago, and I tried searching Google but found nothing that helped. The problem only seems to be with Garry’s Mod, HL2 starts up fine. Also, I haven’t installed any addons or programs after my last session, which was yesterday.

Anyone have any ideas?