try to remove all external device connected to your computer. just leave the keyboad, mouse and monitor connected.
if still a blank screen
remove everything connected to your computer (mouse kyeboard and monitor) restart if nothing happens
open your computer and remove all devices (hard drive, optical drives, memory... restart,,, you should be hearing beeping sounds indicating motherboard is looking for memory. try putting back 1 memory at a time and checking all mem slot. to identify if one of the memory could be causing the blank screen. if both memory will not work try to use known good working memory. if you dont get to hear the beeping sound using a known good working memory. your memory is the problem.
give me more info