Most probably the battery just died.
Batteries degrade over time on its own, and it can't accept current anymore to rearrange the ions. One way is to charge it using a charger with much more current than is specified . I forgot the rating for the C30 but it should be 500mA. So try 2A from a USB charger. If it turns on, switch it over to an ordinary charging method (USB port or USB charger with similar amperage). Even so, it won't hold charge like it used to. If you can't turn it on, don't risk finding an even higher amperage for a battery this tiny. If you can find an electronics expert, have it opened and replace the battery.

Rechargeable batteries don't like having little charge for long periods of time. The chemicals in there becomes useless. The proper way of taking care of any device with a rechargeable battery is to not let the device die of power starvation. I like mine to never go below 20% for every recharge, for every device.

i actually have the latest firmware if anyone's still interested.
I am gonna share it here:

https://drive.google.com/file/d/0B4RACrsvT7...iew?usp=sharing