No display on monitor

I have a strange problem , I have r9 290 with psu ocz 1000w gold , win 10 , asus sabertooth z77 , i7 3770k and 12gb ram
after running windows for around 2-3hours , the display turns off and if I shut down the pc and start it again it doesnt display only there is black screen but every thing is working (fans, power light , cpu light ) , I managed to solve this by changing my gpu slot to another slot but it happens again after hours despite running windows in idle without playing games , I have the latest bios for asus sabertooth z77 , it happens when I go to sleep and left the pc downloading games , it never happens while playing games or on any stress benchmark ,the temperature is fine , find that I must change the card slot and reinstall cmos of the motherboard every day .
 
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