I have the same issue. Ubuntu 18.04.2 LTS was working fine, until I updated and rebooted and now I can't get beyond the 5 dot screen. Sometimes the screen goes to black, sometimes there's no more video signal.

I updated BIOS (Asus A320M-K), put memory speed back to default, removed SATA disks, no effect. I can get into recovery mode, I ran dpkg to repair broken packages but this didn't fix the issue either.

I also have an AMD Ryzen APU (2200G) and I'm using the AMDGPU or AMDGPU-PRO driver (I forget which).

EDIT: I fixed the issue by going into recovery mode, installing Mesa from the Padoka PPA and removing the AMDGPU driver. This might work for you if you also have the AMDGPU driver.