Oh man that sucks I'm sorry. I guess perhaps save up for a semi cheap 80-100 dollar monitor? Preferably one with DVI and/or HDMI. If you google your problem you will find several people that fixed it by not using adapters for your line of cards of the 500 series. I wish you luck on solving this.
So i got a new PSU. Booted PC with new PSU. Tried Unigine Heaven benchmark. Ran fine, no problems. Right after that i get no signal. PC didnt restart or anything, only monitor turned off. Plugged in my TV, it worked. Pc was running fine. Actually couldnt get my monitor to turn on after rebooting and plugging it in and out a few times. Waited a bit, plugged it back on and it turned on. Since then i havent gotten loss of signal. Played some games, it was going very good (need to note that my TV was plugged in too at the same time). Unplugged TV after that. An hour ago i tried Forza Horizon 4 demo, played for about 15 mins - PC froze, screen went black and got that looping sound. Rebooted, got into Apex Legends, played for 20 mins and PC crashed again. Also need to mention that when i try to set my res to 75hz i get green dots on the screen. Pic: https://i.imgur.com/dPdWU0T.png
Now i know for sure that the adaptor is giving some problems, but im not really sure if it can crash the whole PC. But since you have the same problem and you say you fixed it without adapter, it really could. This is the adapter im using:
No adapter here, however I was considering even the most random possibilities and it occurred to me my case was almost 10 years old now. So I went out and bought a new one, moved everything over last night, and so far things seem to be stable. I noticed it would happen pretty much every single time I tried to play Mass Effect Andromeda for more than 5 minutes, but I've been playing for about 20-30 now, so, progress? But the problem has always been intermittent so I'm going to give it a few days and see what happens. Could've been something as simple as old wires connected to all this new tech. I'll report back
Welp, I'm almost afraid to post this but so far I haven't had a single crash! But, I do still get the very occasional audio stutter that would accompany the crash. However 'with' the crash it persisted until I reset the PC. Now it's maybe once every few hours and lasts less than a second, but it does still happen. Not sure if that's a completely separate issue I assumed was related, but otherwise it runs perfectly and I don't think I've ever had a 100% perfect Windows computer so maybe this is just part of it...
I do have a few theories. It very well could be related to Windows 10 specifically moreso than hardware. Why it only affects some people is hard to say but pretty much everyone who has it uses Win 10, many noticed it after an update, and roll backs to 7 or 8 seemed to fix it.
Of course if this new case 'is' what fixed it that suggests it 'is' related to the board getting enough power and not necessarily PSU related. So OP if you haven't already make sure you really secure all your case/mobo connections. A crash like this can also be from overheating so monitor your temps when you play to see where it goes. Between 50-80 is pretty normal for a Vega 64. This case DEFINITELY runs cooler but my temps don't seem to be particularly different.
Anyways I won't get too excited just yet but I've been gaming pretty hard on it and, so far so good!
Hmm which would also suggest tweaking power usage even just slightly could make a difference...
Of course for me at least the problem was sporadic so give it a few days and let us know how it works out!