Weird thing about cod

Hej guys,

This isn't a problem involving hacks or what so ever...
I just downloaded steam, download the game and installed it.

Now the weird thing is, every time I play the game and I close it (quit) ,I can't launch it again...
When I double click the shortcut on my desktop, I get little the steam box wich sais preparing to launch game, it goes away and nothing happens...
When I restart my pc I can launch the game again. Another weird thing is, I can only launch the game right after my pc has started... When I wait 5 mins, or when I go check my emails or something else first, I can't launch it.
Anyone have a idea what this could be?
I'ts kinda anoying, everytime I wanna play codMW2 I gotta restart my pc, unless I launched the game at the start and used alt-tab to do something else
Oh, I also can't launch CSS with my steam...
I reinstalled it like 10 times, just won't work

Greetzzz,

Condy