This is a problem that could have a number of different causes, so I'm going to recommend that you take it to a tech for a professional diagnostic. Generally a white screen is for a bios password, but with nothing on it, then it could be a bios error, or failed motherboard component. I'm going to say that it is a motherboard component failure of some type, but it could be something simple. This nproblem has such a wide variant that it's going to be near impossible for me, or anyone else to diagnose over the internet, (not having hands on), so, again, I'm going to recommend a professional hand on diagnosis.