Black screen to blurry screen on startup

When I try to start my MacBook Pro, I get the regular startup page (Apple logo and loading bar) and then it goes to a black screen with a moveable cursor. I've read a few threads and tried their tips but my computer also does a few things that weren't addressed in the previous questions, so I'm asking again. Here are the differences:

-often before turning to a black screen, it shows a blurry version of my desktop with no icons visible. This stays on the screen anywhere from 1 second to 2 minutes before the screen goes black again

-at this point, sometimes a dialog box shows up saying something like "You shut down because of a problem" and asks me if I'd like to open the tabs I had open when the computer was on with the message that "if you do nothing, the computer will restart in [countdown]". I've tried saying "cancel," "okay" and just waiting, but the screen goes black everytime

-when it's a black screen, sometimes I see a pop-up that says "Link Scanner Shield active," which is what happens when my MacBook boots normally

-my MacBook is making noises that sound like it's starting up

Other applicable comments:

-my MacBook is old... about 8 years now, so I'm sure that has an effect. It was always slow starting up but it's never done this before

-my storage was almost full but not completely full (I kept getting pop-ups that said "Your storage is nearly full")

-this happened because it ran out of battery. I plugged it into the charger, waited awhile so it would start charging, and then powered it on when this happened

-I haven't dropped it, or damaged it in any way prior to this

My nearest Apple Store is over 5 hours away, so any advice appreciated!