The advice to charge your device with a wall charger for a longish period like 24 hours is because making sure the battery is fully charged like that is the first step towards fixing it. It might just be the battery running low despite the green light being on that is causing the issues. Certainly when you reboot it and try to awake it from being frozen that is putting more strain on the battery, and if it's freezing because of stuck indexing books or something, that is also putting a strain on the battery.
The fact that your Kindle us not rebooting when you hold the power button for 20-30 seconds, except for when you had it plugged into your computer suggests it's not fully charged.
So follow the advice above, either use a mobile phone charger or if you only have a USB cable, buy one of those USB wall chargers (
www.amazon.com/dp/B01F2PW4EC/).