@skwirrle this “now it just vibrates once and shows that first ‘Samsung Galaxy S4 (or whatever)’ and blacks out instead of going through the rest of the show. Sometimes it doesn’t even do anything, just stay black, no vibration or anything” would prompt me to start with a new Battery. If nothing else it will at least provide you with a known-well starting point for further troubleshooting which would look like this:
[image|1968997]
[image|1968998]