I am the happy owner (untill now) of a Asus Mobo P8-H77-i, while I do like the motherboard it is inface causing me some problems.
I tried installing my AMD HD 6970 card into the PCIE (only one, as it is a mITX), it shows up fine however: It is only able to give me x4, not the promised x16. I have tried a lot:
-Reseating again and again
-Cleaning the PCIe slot really carefully
-Turned of the auto power saving option (the one which reduces PCIe speed) in windows 7
-Both GPU-Z and CPU-Z gives me the same reading "Link width x4, Max supported x16" and "PCI-E 2.0x16 @ x4 2.0"
-Used the PC diagnostics tool provided by Asus and it passed the PCI-E slot.
-Updated every driver for chipset and BIOS
By now I had reached the conclusion that the GPU must have been a bust, however it worked on my friends mITX motherboard (Zotac Z77) with x16 PCIe bus.. so Im very confused and frustrated.
make sure your intel chipset drivers are up todate. on the mb guild page 2-19 on the bottom is the video card pci slot speed. by default it set to auto. the newer z77 chipset use a repeater chip for the pci 2.0 and pci 3.0 speed. try setting the speed to 2.0 mode. and see if the speed changes. if not check to see if there any missing pins on the mb or gpu. also try using a number two errassor and clean the gold contacts.
Tried the 2.0 mode, unfortunatly did not work. "cleaned" both the PCIe slot and the graphics card with a "fine painting brush" (very, very gentle), same result. Both graphics card and PCIe slot seems spotless, no damage visible atleast.