I have the same board, and had exactly the same issues when upgrading to Win 7. After struggling for hours, I finally had a solution. I flashed my bios to the previous version:
And after a successfull flash, continued to flash again with the latest BIOS,
Thereafter, everything worked SUPER for me, I hope this will help you too.
When you download the bios.exe file to your desktop, right click on it and select 'troubleshoot compatibility', then click on start program (do not close the compatibility screen when the update starts, just leave it open in the background), once it has finished, click on finish still without closing the compatibility screen. Once booted into windows, repeat the same procedure with the latest BIOS. If you do not follow these steps, your computer will say "successfull flash" but if you look at the bios, nothing has changed.
Best of luck to you.
Thank you for your answer/solution.
I will try to do this, the only problem is i've not been able to boot the system anymore, maybe it
will work again tommorow when i come back home and than i will try.