As you are using a hard drive that had Windows 7 installed on it with a different motherboard it will have all the wrong drivers installed for the new motherboard.
Your best bet, and to save a bit of money, is to return the system builder version for a refund (if you can). Then download and burn a copy of Wndows 7 from the link I gave in post 6. It must match the same version that is on your COA sticker which has the Product Key on it. Then wipe the hard drive and reinstall Windows, you should then install all the motherboard drivers that should have been supplied with the new board.
Your best bet, and to save a bit of money, is to return the system builder version for a refund (if you can). Then download and burn a copy of Wndows 7 from the link I gave in post 6. It must match the same version that is on your COA sticker which has the Product Key on it. Then wipe the hard drive and reinstall Windows, you should then install all the motherboard drivers that should have been supplied with the new board.