Linux tyro..., well it is ALWAYS worth trying to get a vt (virtual terminal)
Much can be fixed and trouble-shot from command line
If you can't get vt, either the computer is not booted or video problems, bad display
From X,, press, HOLD control & alt, + F key,, F2 -> F6 (not F1, F7, F8->F12)
Be persistent, maybe because of systemd might have to do twice, try another
Once I had to C-A-F3, C-A-F3, C-A-F2,, I don't know why (I did get vt)
Then, at login prompt, type password to see if looks OK (or locale is wrong or a dead key)
Don't press enter, backspace it away, try to login (both user:password must be exactly right)
Then startx or startplasma or sudo init 5 or ......
If it is a display manager (dm) problem, you may wish to remove sddm & install lightdm
(or, there are several others, nodm, gdm, lxdm, xdm, whatever, use package manager)
Much can be fixed and trouble-shot from command line
If you can't get vt, either the computer is not booted or video problems, bad display
From X,, press, HOLD control & alt, + F key,, F2 -> F6 (not F1, F7, F8->F12)
Be persistent, maybe because of systemd might have to do twice, try another
Once I had to C-A-F3, C-A-F3, C-A-F2,, I don't know why (I did get vt)
Then, at login prompt, type password to see if looks OK (or locale is wrong or a dead key)
Don't press enter, backspace it away, try to login (both user:password must be exactly right)
Then startx or startplasma or sudo init 5 or ......
If it is a display manager (dm) problem, you may wish to remove sddm & install lightdm
(or, there are several others, nodm, gdm, lxdm, xdm, whatever, use package manager)