Did you try to let the battery run down completely? I.e. until the LED turns red then after another 1/2 hour hour or so even that will turn off and the battery is completely empty.
Then try connecting it, reset it and wait for it to hopefully recharge completely.
(I had my own scare earlier when the above happened to me, and it just wouldn't turn on again even with the charger plugged in
Turns that the fuse of that outlet had popped unbeknownst to me... phh... had a vision of brickage for a second there...)
Before that, the battery LED was acting up as well, being stuck on blinking green, but the reader was locked up, and after a reset it turned instantly red: the reader couldn't power back up, thus the above recharging attempt.
Re: Charger. Besides the Garmin one (A/C straight to mini-USB) I also have successfully used the TEKKEON MP1600 I got for $13 from Newegg.com. This one is used with the USB cable that came with the reader.