Nitro 5 Critical Low Battery - will not charge nor open a screen.

I just bought a Nitro 5 Computer. after using it and fully charging the battery, I unplugged the charger. The battery worked for a while, but now it just says critical low battery and will not recharge. There is no inhole on the computer to reset the battery as some have suggested. How do I get the battery to charge?

[Edited the thread to add model name to the title]