I had an old M2N-SLI , an Nforce 5 mobo, I tried to install an ATI 5850 and the system would never boot right....I thought bad vidcard..changed it and the same issue. As soon as I put my old 9800gtx+ the system booted with no issues.
The current crop of ATI card dont claim to be compatible with anything less that PCI-e 2.0. So only 2.0 and 2.1 .
I went out and bought an Asus M4A77d, swapped all my components to it ...put my new card , install OS ..and bingo the system booted right up with the vidcard that wouldn't allow a clean boot before.
So yes there are issues with old chipsets and this newer crop of DX11 cards
(at least ATI brands for me )....
I would get a newer mobo from your brand/chipset of choice and avoid the hassle.
You know you wanted a new mobo as well right?