Wieso man hier alle Posts zweisprachig schreibt, ist mir ein Rätsel, ich halt mich einfach gleich an Englisch.
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(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 Outdated chipset drivers especially have caused some weird (and often isolated) issues for me.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.