Why wont Battlefield: Bad Company 2 start?

I just downloaded Steam as well as Bad Company 2. When I click play, the screen goes white for a second, then disappears. When I checked the task manager, the only thing running was Steam. I tried restarting both Steam and my computer, but to no avail. Turning off the real time scan on my security software (McAfee) didn't work either. My computer should be able to handle it (3gb RAM, 3.0 Dual Core processor, Windows XP). Any ideas why I can't run the game?