Wieso man hier alle Posts zweisprachig schreibt, ist mir ein Rätsel, ich halt mich einfach gleich an Englisch.
(I don't get why posts here are bilingual, I'll just stick with english)
@Bols: Are "all" your drivers (not just your graphics drivers) up-to-date? Check sound drivers, chipset drivers etc. Outdated chipset drivers especially have caused some weird (and often isolated) issues for me.
Disable anti-virus software (not permanently, just to try it out, perhaps even while installing the game). If your hardware is overclocked, try using factory settings and see if that changes anything.