If you google the 970 you'll find 'issues' with it....not the least the inability to access the entire memory on it.
Results vary [as with anything] but from day one the 980 was a far better card....were 4gig actually meant 4gig.
There are just so many ways you can get a black screen [or a BSOD for that matter] that almost always it won't be what most people suggest.
First point of call is always going to be an unwanted/unnoticed driver update that's gone belly-up .... followed by the same with an intentional one....and then comes the hardware....specifically the card itself.
Then connectors...assuming you've been ham-fisted moving things around....
Way down the bottom of the list would be bad sectors on a HD ....that's so last century...
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