Mac Pro 5,1 (4,1) Randomly Black Screening

[microangelito]

So I have a Mac Pro 4,1 which I flashed and upgraded to 5,1 with dual X5680s and for the longest time I have been having a really annoying issue. I mainly use the machine in Windows 10 and when the machine is just sat idle, like watching a YouTube video, using chrome or just basic apps it will just hang, display a black screen (with a signal, not turn the monitor off) and all activity will cease until I hold down the power button and restart. Interestingly it doesn't seem to happen if the machine is under load, such as gaming. Has anyone experienced anything like this before? Any ideas on how to fix it as it's really annoying.

The specs of the machine are as follows:

Dual Xeon X5680s
24GB (8GB x3) Samsung ECC 1600MHz Memory (running at 1333MHz)
ASUS Strix AMD Radeon R9 390 8GB
HyperX Savage 480GB SSD
2x Hard Drives (SMART OK)
Original Nvidia GT120 (For boot options)
4 Port Fresco USB 3.0 Card
Sata III Card (For boot SSD)

This also only seems to occur in Windows, and I have installed and reinstalled it several times including bootcamp and EFI methods, currently running EFI.

Any help would be appreciated.

 

[h9826790]

Running both Nvidia GPU (GT120) and AMD GPU (R9 390) on the same computer at the same time in Windows seems not a good idea.

 

[orph]

may be worth ruining a ram test or just re-seating the ram.
re-seating the drive windows is ruining from (in case of lose connection).
and maybe pulling one of the two GPU's to see if it stops, windows tends to be fussy about mixed brand GPU (boo windows), i had real problems in win 7 with 2 Nvidia GPU's (gt120+GTX770) i assume as there different generations (different drivers?) the drivers got mad at me and crashed or something.

 

[microangelito]

I actually disable the GT 120 in Windows and leave it on basic display driver, so it doesn't conflict as like you say the Nvidia drivers don't play nice with that card. It's actually detected as a 9500GT, but never mind about that.

I'll do a memory test overnight I guess. The drive is perfectly connected, that's not an issue.