I'm a little confused here, you say you're running Win 8.1 64 bit but you have a "Choose OS" screen, is this a multi-OS system? If so, what are the other OS's available.
For clarification, when you say it goes blank after getting to the choose OS screen, is that with or without any further input (i.e. do you select Win 8.1 and it goes blank or you just look at it and it goes blank?)