I have an old Kindle that now won't charge. I have tried different chargers, plugging into mains and USB. The screen seems to be frozen with the battery/charging display. The orange light comes on and then changes to green. I've tried to reset by holding the on/off for 40 seconds but the screen still seems to be frozen and appears not to charge.
I have resurrected several kindles from apparent death. But without knowing the exact model/serial number, it's hard to give device specific instructions. The last two I rescued also changed from orange to green but then froze on the battery charging screen.
Firstly, how long have you tried charging it for? Some of mine have taken over 24hours! Also, for some models, just holding down the power button for 40 seconds isn't the way to reset (for some you need to press and hold both the power AND volume up or down button) until you get a flash on the screen, then you let go. Also, sometimes you have to do that several times in a row (because doing the reset does take a big chunk out of the charge so there's not enough to actually switch on). So charge again and do again.
Also, this may sound odd, but it's worked for me. I have a powerbank that determines that max voltage and speed a connected device will charge at. Often when mains and normal charging hasn't worked, I've connected it to that instead and it has worked. So if you have one or a friend has one ... to my mind it just seems to give it a bit a swift kick up the ....
So I'd say first of all, leave on mains charge overnight again and then try the two buttons at the same time reset, at least three times if necessary. Also it might be worth googling "kindle won't switch on after charging" or "kindle won't power on" and finding the instructions for your exact model ... or even search in youtube? One solution does not fit all.