Why won't my device turn on when I press the power button?

The problem is most likely your batteries are dead or misaligned. In this case, you'll probably want to replace the batteries. For help in this matter, I would personally recommend checking out this troubleshooting page.

A less likely problem, would be the internal wiring has become faulty and the battery harness is no longer supplying power to the motherboard. This repair is more involved but you can also find help on the troubleshooting page.