fullscreen artifacts except in safe mode?

Hi there,

after a gamecrash, my mac pro only boots in safe mode. In normal mode my screen is totally artifacted and I have no way to navigate. What can I do about it?

Screenshot: monitor


Facts:
- I reset NVRAM already, no effect
- Created new user, no effect
- ATI 3870 HD
- OS 10.7.4 with all updates, Mac Pro (2x 2,8Ghz quad core Intel Xeon)
- In safe mode, absolutely no problems at all. However, hardware acceleration is disabled here

I hope this is only a software issue!

Kind regards and thanks in advance,

Thomas