I would check to make sure every cable is plugged in correctly. If they are and you're still having problems try contacting Nintendo and see what they suggest. Otherwise you could always return it to the store you got it from as long as you have a receipt.
Make sure all the wires are in like Syntax said. then if that doesnt solve problem, call nintendo. are you sure your wii didnt fall or get hit or something? if all else fails and you cant do anything, then just take your wii back to the store.