Graphics Card can't detect Monitor and turn to sleep mode

Hi,
I have my new PC for a 4 months, everything worked perfect till one morning I turned it on, and the monitor (SAMSUNG) tried to detect the graphic card (ASUS R9 290) without any success and turned to sleep mode. The monitor works without problems with another PC or Laptop. I connected the VGA card to my tv LG, and it works without problems, after when I connected it back to my monitor, it works, but not stable, in the screen resolution properties it doesn't recognize the monitor, it's going in safe mode for any entering to game, installing some program or restarting of the computer. I tried to put my GTX 650 into that slot (there are 2 slots for graphic cards, and I tried both of them) instead of R9 290, and everything works without problems. So I decided to connect my GTX 650 that works perfect to x16 slot, and the R9 290 to x8 slot... connecting the monitor to GTX650, it detect also the R9 290 without any problems, but when I disconnect the monitor from the GTX650 and connect to R9 290, the monitor going to safe mode again. I tried all these connections with many different cables (all the cables are in working condition).
If somebody can help me, I will be grateful :)
Thanks