Assuming you are using AMD graphics, this sounds vaguely familiar with the lightdm issue, where lightdm will not start but dropping down to tty you can manually start it just fine. The fix is to add the module “amdgpu” to mkinitcpio.
Edit the mkinitcpio.conf file
sudo nano /etc/mkinitcpio.conf
# vim:set ft=sh
# MODULES
# The following modules are loaded before any boot hooks are
# run. Advanced users may wish to specify all system modules
# in this array. For instance:
# MODULES=(piix ide_disk reiserfs)
MODULES=(amdgpu)
Inside the MODULES parenthesis, add “amdgpu”. To save, Ctl+o and then exit with Ctl+x
Next, you need to rebuild initramfs with the following command.
sudo mkinitcpio -P
Reboot and see what happens.