Wow says it failed to find a suitable device... HELP PLEASE!~!!!!?

So i recently had my computer restored to default... too much crap bogging it down, and i had some issues with the wireless drivers.. but my techie buddy jiffied that right up.. now im alone, and my thing wont let me get to wow! its driving me ******* nuts ladies and gents...NUTS my card is a Nividia G-force 8400. and i need help please!