Deus Ex: Good PC, Bad performance

Hello,

can anybody please help me on this issue?

I recently bought a new PC that doesn't have any problem running latest games, but with Deus Ex: HR, the DPS is so low it is unplayble. Even in game's start menu. Changing video resolution doesn't have any effect at all. I tried to update all my drivers by using appropriate software (some kind of driver searcher) so I believe it isn't the drivers. Thank you for your suggestions.

Windows 7 64bit
AMD FX-4100
Sapphire Radeon 6870
8 GB RAM
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