Problem with my refresh rate.

[Riccora]

1. Every time i start the game, my refresh rate goes to 50hz but my natural refresh rate is 60hz.

2. By the fact i got black border.

3. I'm running 1920x1080, Windows 7(64bit) sp1, Phenom2 955, 8gig of ram and hd6870. Nothing is overclocked!

4. To have 60hz back i need to change it in Catalyst (12.10)vers.

5. I tried to reinstall the game and my graphic card driver.

Thx for all help and sorry for my bad English(its not my first language)