I don't know...you're saying it displays the boot up sequence, but doesn't display the game. That doesn't make sense does it?
Hardware issue?
That sounds like maybe a problem maybe with the video card on the MPU - where the VGA video harness plugs into?
(The bottom touchscreen uses the DVI harness.)
Wiggle the VGA plug while on...maybe it's just a bad plug or look for a bent/folded pin inside the VGA plug housing?
I know you said it displays boot-up but maybe plug a laptop into it and see if it works duplicating your laptop's desktop screen?
Maybe a software issue?
If you install back in Bier Haus, does the topbox work again during gameplay?
As you can tell, try checking everything...wiggle connections, try other software, swap MPU's, video cards, or video harnesses...don't give up.