Question RX 580 problems after installing drivers

[Vecto]

Hello. I have problems with RX 580 after I install drivers. Without drivers it works fine but it can't run any game at more than few fps. The problems are:

-Small light blue squares appear on the screwn, mostly on white backgrounds
-Sometimes screen goes off than back on, same way it happans when you unplug and plug HDMI cable.


What I tried:
I have tried many drivers and new F81 bios (it came with F80).
I tried drivers from AMD and Gigabyte site.(20.1.3(latest),19.9.2(recommended),17.8.1(the one from gigabyte website)).
I have tried reinstalling windows 10 and it didn't help. I am curently trying windows 7 but I have to update it to be able to install derivers. My windows 10 is updated and ther are no more updates. Artefacts do not show in bios. I have tried other PCIE slot (both are 2.0 X16) bith with no success. Tried other 8pin connector and it's the same. And I forgot to mention that gpu usage was stuck at max while memory usage was normal.

Specs:
Windows 10 PRO x64 ver.1903
CPU: Intel Xeon E3-1220 3.1GHz
GPU:AORUS RX 580 8gb Rev. 1.1
MOBO: Asus P8B-E/4L (PCIE2.0 X16)
PSU: Fujitsu 760w
RAM: 8GB (2x4GB) 1333MHz SAMSUNG ECC
SSD: Kingston A400 240GB
HDD: WD Green 1TB 5400RPM
Monitor: Samsung SyncMaster BX2231 1080p60hz

 

[Calvin7]

UEFI is a is an improved version of the BIOS Legacy mode. Your motherboard lacks this newer type of BIOS which causes compatibility problems on new up-to-date video cards. I would suggest using an older model video card that works with a legacy BIOS.

 

[Vecto]

UEFI is a is an improved version of the BIOS Legacy mode. Your motherboard lacks this newer type of BIOS which causes compatibility problems on new up-to-date video cards. I would suggest using an older model video card that works with a legacy BIOS.

It says that this motherboard supports uefi but for me it's running legacy and I've read that most people say that it should work in both UEFI and BIOS