Hi @delfyr,
Have you checked the display when using Windows in safe mode or when viewing the BIOS menus of the PC?
Just wondering if it is a driver problem as when Windows is in safe mode or when looking at the BIOS menus only generic vga drivers are installed and not GPU hardware specific drivers
If it is OK in safe mode (or BIOS) is a separate GPU card used?
If a separate GPU card then does the PC also have integrated graphics on the motherboard i.e. CPU with graphics capability?
If it has try that. It could be a faulty GPU card or a video driver problem