Nope. It's just a genero install.
It does sound like the motherboard, but its strange that its even working at all. Just a shot in the dark here but do you have any kind of throttling options in your BIOS that restricts CPU speeds/voltage?
I am not familiar with your chipset or BIOS but did you have to overvolt it much to get it to hit 5Ghz? Maybe you have cooked it a little. As a complete last resort you could flash the BIOS? Not something I would recommend though if you have the ability to RMA it.
Sorry to be of little help, its a weird problem indeed.