If you have a retail version of windows you can just re install it. Although if it's OEM it's fixed to one motherboard. Try to press F8 when you are booting so maybe it will allow you to go into safe mode from there you could try do system restore if not I'm afraid you will have to re install it and if it's OEM new copy of windows ( note that windows 8 is not fixed to motherboard but a user so you can move it form one motherboard to another.