Actually, it seems it is booting, only not into X-Windows.
Could be the kernel you are using has no hooks for the amdgpu.
What you can do is use: Ctrl-Alt-F3 and go to a console and see if you can go on troubleshooting from there (would be a regular text console).
Before you do that though, go into /etc/default/ and edit the file “grub” and change the timeout settings:
GRUB_TIMEOUT_STYLE=menu
GRUB_TIMEOUT=3
GRUB_CMDLINE_LINUX_DEFAULT=""
First line will present you a menu of found systems. It should also let you boot into recovery.
Second line will give you the time to actually see the boot menu (you can set it to 5 also).
Third line will tell it to be verbose. To show you stuff on the screen.
Once the file is edited, run:
$ sudo update-grub2
It should regenerate the grub boot loader with these options.
PS: That will only work after you rebooted after the installation, as during the installation, the / filesystem is mounted somewhere else for installation.
PPS: If you can get into the CLI with Ctrl-Alt-F3 - you can also apply the changes to the grub configuation!