Re: screen goes completely black after 20 mins
First off, uninstall your graphics driver completely and use windows for a few minutes (or hours), it'll be slow but if it shuts off then, then you know its not a graphics driver problem. If it does not, then you know that the drivers are the source. We do not have enough information at the moment, so just try that first and tell us how everything goes.
Good luck, Huza08!