Having an issue that pissing me the hell off.
I start Alien swarm and it goes to a black screen as if its about to start. I wait about 10 seconds and then I see it just quit with no warning, errors, or anything..

Any Ideas?

I'd do in the order.

1. new video drivers.

2. check the steam forums

3. reinstall Alien Swarn

4. check power supply

Inbetween each number run Alien swarm to see if any of them worked.

My vote is for 4. -- definitely sounds like a power supply.

I took out my power supply, swapped it out with another one, as you know the recommend 200W.
I also uninstalled every steam related thing on my computer and reinstalled. It at least starts now :P

yea, i had this exact same issue except it was just alien swarm, it was any valve made game. i closed steam, deleted the usual files, the 2 .blob files, and restarted my computer and than steam and it works now. very odd.

Yeah, I had huge CS problems as well. Blowing away EVERYTHING steam related and installing in a complete different folder (to get rid of any reg-key nastiness) made my shit run wonderfully

anytime i uninstall programs (there are a few programs that dont work well this way, symantec products, and apple products) i use Revo Uninstaller. it runs the built-in uninstaller, than it scans ur computer for left-over registry entries and files (always run it in the advanced scan method, no or barely noticable speed difference, but does a deeper scan) and gives u the option to delete all or some of them. the best uninstaller i have found. there is a pro version, which oddly enough can be downloaded for free through the basic version and used (dont remember if there are restrictions on it tho), but the pro version, while having more viewing options and more added features, only crerates a system restore point b4 every uninstall (by default) which takes FOREVER (i dont know why, but it does).

Verify your game when/if that happens again. You were probably missing a file. Tucker had a problem the other day with his Source doing something strange and told me about it, then I had a problem with Alien Swarm and I remembered him telling me that fixed his problem, turns out that I was missing like 30 files.

i did that. none of my valve-made games would open (open that black screen then desktop with no error), i tried verifying a couple of them and it didnt find any problems.

I also deleted all local files and tried again, but it didnt work till i removed all of steam and anything with it and installed in a completely different folder... If it happens again I'll try the verify.