if its a bad power supply or motherboard then your pc would just crash. There are several reasons though while you might get a black screen
1. bad or lose Display cable)
2.Bad or lose POWER CABLE ( not display)
3. Driver issues ( Check event viewer for display driver crashes)
4. Possible other unknown software
5. Power supply issue ( Normally your pc should crash her or something, or even start. Not sure what kind of PSU you have and how powerfull it is. In general it is always a good finger rule though to calculate power consumtion like this : 350w Mobo, + GPU usage ( this is a bit differenbt but lets be on the high site and say 150-200w there) on top of that you should claculate 100w for usb and other passive cards or HDD/SSD So in general if you have 600 Watt PSU you should be mee on the edge maybe but it should work. If you have 700 or above you should be pretty save from any power issues ( I like to overkil my because i lower the strain on my psu so i installed a wooping 1200w in my pc) Most Displays have today ther power supply build in and those work or they burn down your house .. there is not sometimes yes and then sometimes not unless the power cable is not sitting good in it.
6. GPU Issues: those are rare. Most comming thing though with what you descripe would be maybe an minor issue with the port. Changing ports on your gpu gives normally a good indication. Other GPU issues are normally seen as artifacts etc. Anything beside that should normally trigger a driver crash actually . But you can sort of check that if you have checked anything else i mentioned above already.
a. Is this happening also when the pc is on idle ? (shake cable. monitor etc , just dont shake your main pc directly )
b.Check internal cable from the psu to the gpu (when the computer is turned off)
c. Run a benchmark as long and often as possible
d. report back to me with the results .. the more details you can give me what each thing did the more i can make a guess .
Beside that i cant really think of anything else.. Unless russia has hacked your pc and they are connecting to it