What's your hardware? The guts that make up your machine. PSU, gpu card, Mother Board, how much memory, monitor and attached peripherals (#2HDD). Are you using a UPS unit or power strip?
I agree with juanrdp. Sounds like a power problem. The way to test it is to replace the RM650x with a spare PSU or borrow spare power supply. I owned an RM750 which had the same problem. It had a bad automatic fan setting back in '2013. After 6 months, it started black screen crashing. Randomly at first. It gradually increased the frequency of black screening crashes till it fried up. I went to Corsair's website to get an RMA and found that the model I had was recalled for a faulty fan setting. It was overheating. Corsair sent me a new one which is still running.. . in someone else's computer.
-Before you try that, have you reseated all your hardware? Sometimes the connections get dirty and needs to be reseated. Take everything apart and clean of all connections by plugging in and out a few times. GPU card, ram, all wired connections.
-A game often remembers a crash. It's like a game setting in the menu. Reset the game and reload all your settings. Go into the game menu and select 'default'. I sometimes uninstall a game if I can't find a way to default it. If you remove the game, make sure it's a clean uninstall. I use a third party cleaner like Revo unistaller. It's free to use for a month. Remove the game completely.
-It could be a Windows problem. Crashing or sudden shut-offs wreck a PC so Windows could be damaged and needs repair. In Windows 7, Go to computer> right click Local Disk(C)> Properties> Tools> Error-checking> Check now>
check both boxes> start. Let the program run.
-Run Disk Cleanup and Defrag it.
Hope this helps.
Tom's Hardware as a PSU tier list if you wish to check out their recommended (best and worse).
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html