Just read through all of this i'll summaries to what i understood of it, let me know if its right.
EDIT: It wasn't installing the drivers it happened randomly and I tried fixing it by installing the drivers.
What happened randomly? The flickers? If so, i understood the flickers were happening randomly with the old drivers. You updated to latest drivers to try and resolve?
The flickering doesn't start when I play a game it starts right when I boot up, and it isn't a bad cable, because it works perfectly fine in safe mode, it has to be a software related issue.
So the flickering starts during post? If so, it's not software related here unless i read that wrong and you meant as it's booting to Windows loading screen when gpu drivers start to load.
If i'm right in assuming the gpu flickers at post and the flickering was happening with previous driver, it may well be the card is not healthy.
Just to share some experience of mine with flickering with a Displayport cable i bought (2m) even though apparently HBR2 Vesa certified, it was flickering on me at 1440p@144Hz. Lower resolution/less Hz was fine though, just pushing the bandwidth was too much for the cable's quality. The 1meter cable Acer supplied works like a charm. Thought i'd share just in case you did buy another monitor cable if using Displayport. You could be having multiple problems happening simultaneously.