New logic board causes my bootcamp screen to be black.

Hey there, my MacBook Pro 15" (early 2011 - Radeon 6750M) stoped working (no battery, no charge and could not charge it) I send it in to repair and got it back two days ago. It works fine now, but when I boot it up in Windows 7 (Boot Camp) the screen becomes black at the login screen, I've tried to put a secondary monitor on (Thunderbolt->VGA) and it works fine, but the screen on my MacBook Pro still remains black no matter what sreen options I try (resolution and extend/mirror),

I've tried to install the Windows Bootcamp drivers again but it didn't help.

Anyone who know how I might get the screen on my MacBook to work?

Sincerely Adam.