Hi @FixkaCZ
1st try to uninstall every VGA driver, even ACC, MAB
system restart
download and install updated drivers
after that, change Core MHz, to 950 MHz.
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About Windows 10:
The best to do its to install fresh one. I mean download W10 and wipe out the whole system.
I dont know how many HDD do you have, but if 1:
During the W10 installation do total format
Create 2 partition, 1 for the op system, 1 for the games
The op system will need around 200-250 GB disk place
After system related installs, instal origin for example:
C:/Program Files (x86) change C to D
If you have 2 or more disk, wipe out the system and the game disk, you will need it because W10 is more different then W8.
PS: Dont forget to save all your important staff to external drive. Porn first... 👿
If you have any question about install, pls PM to me.
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HDMI the better option, is it possible the cable is dodgy or the connector in the monitor...try other one if you can or.... the monitor itself is not full HD...