The normal solution, in this sort of scenerio, would to reset the BIOS to default by taking out the “coin” battery forcing the BIOS to its factory settings. Unfortunately, the Asus ROG G20AJ is a bit of a lemon in that the case is very hard to open and then once opened the motherboard and all its components are very hard to access.
Perhaps take a look at the BIOS screen. Is there a default setting option?