Re-check all your BIOS settings, and make sure that CSM is disabled. You may also need to update the Intel Management Engine (ME) Firmware. It's under Driver > Chipset (on the same download page where you got the BIOS from.) Another thing worth giving a shot might be a clean install of the graphics driver with Display Driver Uninstaller (DDU).
Also note, with some motherboards it can happen that you only need to go into the BIOS settings, then choose Save & Exit without actually changing any settings. Doing this could potentially update some entries that exist within the Serial Peripheral Interface (SPI) flash memory, or non-volatile memory (NVM). (This piece of memory is also commonly referred to as "SPI NVM".) One of the most common example scenarios when you might need to perform this step is after you change out your RAM. However, sometimes, after a BIOS upgrade you might need to restore the BIOS settings back to factory default, then go into the BIOS settings again and redo all the adjustments (tedious, but sometimes necessary to get everything working normally again).