Dual HD6550D + HD6670 Stopped working

Hi, two weeks ago I managed to build my new PC on the Mini-ITX platform using the ASUS F1A75-I mobo with the A8-3870k APU and Sapphire HD6670 Low profile discrete GPU.

After some initial truggles I managed to enable the Dual graphics mode like the guy here: [url=http://www.tomshardware.co.uk/forum/340770-15-enable-6550d/][/url]
Then It was working fine for more than a week with good performance. Recently I tried to squeeze out some more performace by raising the base clock frequency and playing with the multipliers but without any success (Instability issues) so I went back to stock settings. The dual graphics was working.

Yesterday I tried to overclock with different RAMs and a stronger power source but again I got only instability so put back the previous HW and let the idea of overclocking go for good.

Unfortunately soon I noticed signifficant decrease in graphics performance and realized that the Crossfire option is no longer availabe from my CCC menu. I tried to reinstall the graphic drivers, tried to set default bios settings, even reset the CMOS, flashed a new bios from the ASUS site but noting helped. The Dual graphics otpion does not work anymore and I am stuck with either using the discrete or the integrated card but not both together.
What is strange, I also tried this: http://www.tomshardware.com/review [...] 975-2.html and I was able to enable the Dual graphics but I dont think its a correct approach in my sittuation. The performance was lower than before and I dont have any graphic output when booting up. The original ASUS approach is to use the Integrated GPU output and it aws working fine.

Is there a possibility I have somehow damagegd my mobo so it wont allow to enable crossfire anymore?
Do you have any advice please? I am thinking of replacing the MOBO with a new one.