Trouble Turning On + Apps Won't Load?

Basically what's going on is that I have trouble turning on my phone; it either gets stuck on the loading screen, takes me to a screen that says 'android is optimizing your apps' (or something along those lines) or gets me to my lock screen, where it normally crashes and takes me back to problems 1 and 2. But sometimes I do manage to get my phone on where another issue takes place: my apps don't show. I have the default ones and like two third party apps that don't open when tapped on, and the rest are completely gone, and in my storage the SD card is a no-show. I only have access to my bookmarks in Chrome, as my keyboard won't pop up either. I've tried rebooting my phone normally (didn't work) and I tried to do safe mode (didn't work also) and I don't mean to be redundant but the problem takes me right back to the beginning: it won't turn on.

Right before I started to get these problems I had an issue with the System UI (that's what the popup said) constantly crashing and at times my phone would completely shut down. I heard a factory reset might help but I'm a bit hesitant because it takes away everything so I want it as a last resort. Any help is really appreciated because this has been a major inconvenience.