Hey, Kyle. This can be caused by a couple different things. The first place to check is the battery. Remove the battery and inspect the three gold terminals for signs of corrosion. Then inspect the corresponding terminals on the board. clean these carefully and reinstall the battery.
If that doesn’t fix the problem, you’ll need to open your device further and check the two ribbon cables on the board (or any of the other 6). Based on what you said about the popping noise and the pressure of your backpack I would say this is most likely your problem. You need to make sure the two gold colored ribbon cables aren’t loose or damaged and that the pins on the board are also not damaged. Be gentle with the cables. If the cables are properly seated your screen is likely damaged and will need to be replaced. Let me know how it goes. Hope this helped and good luck!