I can launch the game without issues but when I start the actual game all I get is a black screen, although I can see the crosshair, the audio is present and I can access the menu.
What could be the issue here?

I'm running on WIn 7 64, i5 3450 and HD4850, if that's of any relevance.

Yes, I have.

Actually I just managed to solve the problem by reloading the level from the level select screen and the issue seems to affect only the tutorial anyway.

Just wanted to mention that I had the same issue, and Smertnik's suggestion fixed it.
If I start a new game, the tutorial level just loads a black screen with a green crosshair in the middle. If I set the image quality to 'crap' or 'ultra crap' in-game, instead of a black screen the screen flickers rapidly. If I press ESC the pause menu shows, then if I choose Level Select>> Tutorial it works fine.

Running Windows 7 64bit, ATI HD7970 (driver v13.1), and I reinstalled Directx 9.0c