I have this problem ocasionally since Win 8.1, so not to blame Win 10.
Some times it justs starts Windows in low resolution and it lets me change back to full HD. Other times it totally goes to VGA...

Spent some time trying to solve this. Did a lot of changing video drivers but it all solved after unplugging and rebooting.
First time it happend to me.
radeon 7830 and dell ultra sharp, vai...