Hmm odd graphic intensive progs..

intermittant... .. yeh ..

It is VERY probable that circuitry in the monitor is on the fritz.. how old the monitor?.. if the monitor is close to its specifications with the resolution it is running.. you can and will get that symptom.. typicly when the line osc is out of sync.. ..

Certainly follow the good advice given.. check your cables, check your video card... PAY ATTENTION as to when this happens.. HOW long has the PC been running.. is it in the middle of the day, late at night.. is it HOT or COLD in the room..
When the symptoms appear.. wriggle the data cables at the back of the monitor.. then at the back of the tower.. slap the side of the monitor (seriously.. about bitch slap hard.. stinging hand not hurting..oh you dont want to knock the monitor off the desk.. it could land on someones foot)..
On the video card end of things.. I would only fiddle here after you have cleared the monitor and data cables and connector.. I asked about heat before.. be aware that a video cards can have cooling fans.. thes can and do fail.. causing over heating and the all video stops..

WAIT: Question.. When you lose Video.. HOW do you get the display back? is it after a complete shutdown? do you have to leave the PC off for a while?..or just a simple restart? what?