About two weeks back I decided to change my graphics card. I bought a "Gigabyte AMD RX 580 AORUS 8GB" and installed it. Ubuntu then stopped being able to boot up so I reinstalled it from a live CD. It then booted up normal. However, ever since then Ubuntu completely freezes after being logged in for about 5-10 minutes and the only way to "fix it" is to manually shut down by holding down the power button (Alt+F2 or Ctr+Alt+F1 through F8 and Alt+SysRq+REISUB all fail). I have tried installing amdgpu-pro but it experiences the same problem. The only constant solution has been to boot in recovery mode and then resume normal boot in order to get to low level graphics mode. My question is therefore, how do I make this (low level graphics, llvmpipe) the normal boot option for Ubuntu?
I am running Ubuntu 18.04.1 LTS.