I recently upgraded my motherboard, which may be coincidental. But I never had this issue before. Now, after a reboot, if I try to open a Steam (or any) game on my main monitor. which is a Sceptre Widescreen running via DP, the main goes black while secondary remains on. My secondary is an older HP with a DP->DVI adapter. If I unplug the DP running to my main, and plug it back in again, it seems to come back up and stay on. But if I turn off/put to sleep my PC, I will have to inevitably unplug the DP cable and and plug it back into the back of the graphics card for it to come back and stay on. This ONLY seems to happen when I have a video game running on my main. I can dual monitor all day with web apps open. But yeah, as soon as I open a video game, I have to un/replug. Its extremely annoying.
Like I said, this didn't start happening until after I installed a new motherboard. So I had this same exact setup (besides the MB) for over a year, with no issues until this week. First run with the new board, I fired up Cyberpunk, and noticed the screen kept cutting out. I thought it was CP, since its known to be a buggy game. But now its happening with every video game. Sucks because I like to have walkthroughs open, or keep an eye on Discord while gaming.
I've tried different DP ports on my GPU. I have tried turning off HDCP in Radeon Settings. I have updated Radeon software to most recent version. I don't know if FreeSync is the issue (just turned it off and will reboot to see what happens after posting), or if the cable is bad. But the cable is practically brand new, and never gave me issues before. FWIW the cable is the one that came included with my Sceptre monitor. Maybe that is the issue. But since it worked for months before with zero issues, I would hate to spend $20+ for nothing...
Here is my current set-up:
ASUS TUF Gaming X570-Plus-Wifi (new as of a week ago)
MSI Radeon RX-5700 (flashed with the XT bios, which I did several months ago, long before issues arrived)
AMD Ryzen 7 2700x (with Wraith Cooler)
Corsair Vengeance LPX 16GB (2x8GB) DDR4 DRAM 3000MHz C15
Thermaltake SPD-0700NP 80+ Smart 700W PS
SK hynix Gold S31 500GB 3D NAND 2.5 inch SATA III Internal SSD
WD Blue SN550 NVMe 500GB SSD (also recently installed).
**UPDATE** Aaaaand, just like that, I think I may have fixed it by turning off FreeSync. I don't know how bad it is to be missing out on Freesync. But maybe it could still be used, if not Dual Monitoring. Anyone know if having FS turned on has caused similar issues with using a second monitor while gaming? Does anyone have any fact based opinions ON FS? Is it worth it to turn on, or is it crap and make things worse. Anyway, hopefully the black screen issue doesn't return, and then its back to the drawing board..