The very first thing that you want to do is go the the Asus site and check to make sure that the BIOS on your motherboard is the most current one available. (Actually, I'll do that for you, but you should learn where it is. A7N8X-X, A7N8X, A7N8X Deluxe all seem to be at 1006. The A7N8X-VM is at 1008.)
NOTE: Just because the motherboard was just purchased it doesn't mean that it has the most current BIOS.
The other thing that could affect things is if the memory is being recognized incorrectly. I have had that, in the past, cause a problem with the CPU recognition. Try switching out the memory if you can and see if that helps.
Also sometimes the CMOS can get bad values in it. I have found that on certain RARE occasions it is helpful to erase the CMOS. Usually there is a jumper on the motherboard for that, but often I just pop the battery and wait 1/2 hour. Put all back together and see.
That's my help.
(It could be a bad CPU, but I have not run into that ever on an Athlon CPU. They either work, or don't, they don't generally report to be a different CPU in my experience.)
Hope that helps,