Can't Turn Off - Stuck on 'Fully Charged' Screen

I replaced both the battery and the headphone jack on my iPod classic thin. It was working absolutely fine for the first few days but now it seems to think it's connected to a power source even though it is not.

When I try to turn it off it goes to the charging screen and says it is fully charged. This then drains the battery as it won't turn off.

All functionality is otherwise fine, just can't seem to get past this problem. Tried fiddling around, resetting it and a couple other things and am now out of ideas. Help!

NOTE: That problem seemed to resolve itself and now it is completely dead. If I plug it in it will flash the apple logo and will promptly die when unplugged. I'm really hoping it's not the hard drive. I've done everything I could think of and looked through all the other questions like this about the classic and have not found a solution. Before it died it did make a clicking and whirring noise every once in a while (which I think is the hard drive) Any ideas?

I have already tried the following:

- plugged into compy

- plugged into outlet

- tried to reset

- tried to put into disk mode

- opened up and checked battery connection (all good)

- cleaned with isopropyl alcohol

- cleaned with air duster