Start up problems... yes I’ve tried that

Hi! So my computer won’t finish starting up. It’s typical MO is to load the progress bar to 50% and either go to the Grey screen of death or power off and restart itself in a cycle.

I have tried:

command + R

shift key (safe mode)

option + command +R + P (for exactly 20 secs)

option + command + control

nothing has worked. It will either get stuck in the loading screen, or go to a dark grey or light grey screen of death. Or it will Shut itself down and reset itself. I have never gotten it to bring up any other screen.

can anyone help me????