Freezes & BSODs Even After fresh Windows Install

Hello folks, I’m having some PC issues and was hoping someone could help me fix them! Last Friday I swapped an Asus HD 6770 for Gigabyte HD 7850. It seemed to work ok in Windows but crashed / froze in all games, benchmarks and when playing HD video. It would either crash to a black screen, or a green screen with dark green vertical lines. I tested it with the last 5 driver versions inc...