Troubleshooting Kindle 4 NT restarting by itself

[Kszyniu]

Hi, I'm having a problem with my Kindle 4 NT D01100. It was laying unused for a few years, however it was not damaged. I tried to run it again, but there is the problem. It charges and runs normally, however it freezes and then restarts by itself every 5 to 10 minutes. Here is a list of other sympthoms:
- It can't find any WiFi network; shows (0) WiFI networks available - same with 2.4 and 5GHz ones.
- Every time an action is performed (like turning a page or opening menu), it makes a silent buzzing sound, similiar to those made by HDD drives if you know what I mean. Every time it freezes before a restart the buzzing sound stops.
- The battery holds only about 1 day
And also a list of what I've already done:
-Factory reset
-Uncharging the battery to 0% and charging it to a 100%
-Disassembling it to check the internals, although everything seems fine there.
- Unregistering it and registering back, however I can't register it back as WiFI doesn't work
At this point I have tried probably everything I could find on the internet, however nothing worked. The software version is 4.14 so I think is up to date.
I've been thinking about replacing the battery, however those are kinda expensive where I live and I'm not sure if it would fix the problem.
I hope to find some help here, although I am aware that my Kindle can be simply dead. Thanks in advance for any advice.

[Quoth]

worn out LiPoly cell (aka "battery"). Time and heat wears them out as well as charge cycles.