HL:S doesn't run

[NJspeed]

Just downloaded HL:S today. I got it to run once but it crashed as soon as I changed my video settings. Hasn't run since. It actually doesn't even open. The screen flashes for a second and then theres a window that closes down to the Steam box on my toolbar. I deleted the game and redownloaded it, still nothing. I had Steam verify the files and that didn't work either. I don't know what else to try.

HL2 still runs fine.