Glitches and screen flickering after install

Hi!

I installed High Sierra on my PC, the installation went fine but the screen is flickering after the installation. A picture will describe the situation better than with words: https://imgur.com/a/llu42

My specs:

GPU: Nvidia GTS 450

Motherboard: ASUS P8Z68-V Pro

Processor: i3 2120

Memory: 16GB DDR3

I installed the Nvidia Web drivers for my GPU (http://www.nvidia.com/download/driverResults.aspx/126538/en-us)

My bootloader is Clover and I enabled the Nvidia Web Drivers. I also added the NvidiaGraphicsFixup and Lilu kexts

I installed Yosemite some years ago on the same build

Any help would be appreciated!