Frozen screen, Kobo Glo HD E-Reader: what is the issue?

The screen on my Kobo Glo HD is frozen

Model: N437

Details:

• When i press the power button it sometimes flickers a little bit (ink shifts slightly) but this is very inconsistent
• The frontlight seems to still work at least partially, when i press the button it sometimes lights up for a while, though the behavior doesnt seem consistent.
• Althought I don't know for sure, I doubt the battery is the problem because this issue started to occur within a year or two after i bought the device. In fact it was within the warranty period but I was too lazy to send it in back then so it has just been collecting dust in my wardrobe for several years now.
• I'm pretty sure I never dropped it or got it wet or anything, it just seemed to die spontaneously during the night so when I woke up one day it was frozen.

What I tried:

• I have tried holding down the power button for 15 seconds
• I have tried pushing the reset button
• Keeping the charger in doesn't help

I uploaded a video clip.

What do you think the issue is, and has anyone had the same issue? Is the problem the battery, a broken display, something else?

Thank you for any and all help =)