I am attempting to replace my Windows 10 install with Ubuntu 18.04.4. I had managed to successfully do so, but due to what I think is an incompatibility between my current graphics card (TAHITI ATI/AMD Radeon HD 7870).

The reason it seems that way is because when attempting to even boot from my USB disc (which had the ubuntu boot image), it would result in a black screen and I would be unable to install. Similarly, post-install, attempting to simply boot would result in the Ubuntu load screen (with five white dots) flashing on briefly twice, before going dark and hanging. A passing reference to incompatibility between AMD Radeon hard drives and Ubuntu was noted, and the way I've gotten around this is by editing the boot instructions in grub ('e') and putting in 'nomodeset' before 'quiet splash'.

However, this is not an adequate fix. This results in me being locked to a single monitor, locked to a very low resolution (some 10XX x 7xx). The idea is that I should take this time to install the drivers relevant for my graphics card, then rebooting should fix the issue, but so far, it doesn't seem like the case. Moreover, according to documentation for the the Ubuntu open source RadeonDriver, it seems it should be immediately compatible with my graphics card, which I'm not sure it is.

I'm at a loss. Since I've replaced my Windows install it's not like I can just go back to it (and I don't want to), so I need to figure out how to get Ubuntu to boot properly and leverage my graphics card.