half life 2 episode one problem

i got half life 2 episode one and whenever i try to play it, it goes to the valve screen and some copyright stuff and then it goes bak to windows. i didnt have this problem with playin half life 2 cause it was workin fine. so wasit problem?

 

Your downloaded version could be the problem *Wink*

 

Or..

There has been a update to the game aswel.

try applying the update.1