i have the same motherboard, but the micro version, i know the answer to your issue.
IT IS THE BIOS
maybe not the latest one, but an older version has info indicated the correction. I had upgraded to 8GB as well (i thought my old memory was bad) and the issue ended up that it was my MB and my MB got replaced, the replaced MB would not do anything (^^^^^^^^) so I backed off to my old 2GB modules, BAM it worked, booted to windows, flashed bios, shutdown and put in the new 4GB modules - worked like a charm
ASUS flash bios program from windows works just fine