I'm playing Left 4 Dead for a while. But the problem is it suddenly stops without any notice and desktop appears. Sometimes it happens after covering 2nd stage and sometimes after 3rd stage. There is no error message no freezing state just desktop appears. Something like desktop is emerging from the game.
I found on the net that it requires 7.5 GB space whereas the dvd of Left of dead that I have got contains 4.39 GB.
I can play call of duty 5 easily.
I'm using ATI Radeon 4890, 2 GB Ram and Core 2 Quad 9400, XP SP 2.
That DVD is using compressed data. Even on Steam downloading it is only about 4GB because of the compression VALVe uses.
Try doing a cache verification of the game files. To do that go to Steam then right click on L4D, go to Properties, then Local Content and click it. It should check the game files and make sure they are all there and corruption free.
Then try the game and see if it works.