Shut it down and bring it back up in safe mode. If the monitor still goes out to lunch it's the monitor, or video card/MB,( I say MB only if you plug your monitor into the MB). If the monitor stays on insafe mode, you need to think about when the problem started, and if you made some changes to the pc ( like adding new or different hardware, or new software). Does the operating system load to the desktop before the monitor takes a hike? If not you could have a resource conflict that would keep the video drivers from loading.
Good luck with it!