I'm getting the same thing. I added a bunch of mods yesterday, and last night was getting a very brief error message about needing Heathfire to get the mods to work. I thought what the heck, it's only 5 bucks, so I went ahead and bought that. Not sure it ever installed properly-- I don't get that error anymore, but when I try to load the game, I get the Bethesda screen and first couple drum beats, just a glimpse of the Skyrim dragon screen before it shuts down. I can't make Steam itself open at all... support opens, but that's a whole different deal. Needless to say, I've disabled all the recently added mods to no effect. EDITED TO ASK: Did anyone else have a rather large Steam update in the last couple days? I suspect that the root of my problem lies there...