I'm at a loss. Google'd and watched some YouTube vids without a solution.
I have an LG G3. In good shape, been using it for a couple years now, never any issues. Several days ago I downloaded Empires and Puzzles (a game from the app store, highly rated, no mention of issues in the comments before I downloaded it). Been playing it quite a bit for several days without issue.

Was playing it tonight, battery at about 60%, and the message "LG System Server has stopped working" and the phone went blank.

I tried holding the power button to turn it back on, nothing happened. I tried removing and reinstalling the battery and this did nothing either. Plugging it in to 2 different chargers had no effect. Went to Google, read some things.
Removed battery, held power button for a few seconds to completely drain phone, reinstalled battery, held power button and I get the opening loading screen from LG for a few seconds, but it goes no further than that. This is where I am stuck.

I've read about a Factory or hard reset, but I have not been diligent with backing up my phone, so contacts, texts, pictures, probably most importantly my calendar events such as dr appointments and whatnot, are all stored on the phone and I don't want to have them wiped off. As I was searching for answers and typing this last night with the phone on the desk beside me, I noticed that it eventually goes back to the LG powered by Android opening/loading screen every once in awhile before going black again. I don't know if it is continually restarting or what.

I'm hoping you have a solution to this or can point me in the right direction. Even if there's some way I can back up the phone and do a hard reset without having to turn it on that would be great, as long as I can save the information on the phone as of this week. It's especially worrisome because I recently had to put down one of my dogs and all his pictures are on this phone... I hadn't brought myself around to putting them on my computer yet of our last hours together.