iPod - iPhone people. The best trick for a "broken"( won't power on, frozen, app failure, crazy slow, etc) device is to re-set it. Re-setting does not mean to turn it off. For iTouch and iPhones it's the same... hold power and home button until your phone powers off and reboots. Do not let go until the apple logo shows up on your screen. This fixes most problems.
Other issues come from crappy down loads of apps, either delete and re down load or delete app from device.
If this doesn't solve the issue do a complete reset in iTunes then back up from previous backup.
If this doesn't work take it to a Mac genius. They will trouble shoot it and if it's within it's warranty and there is no water damage they will give you a new replacement in store; if they didn't resolve the issue.
iPods reset is holding the middle button and the pause play button till device powers off and resets. Again don't let go until the apple logo appears on the screen.
For all devices... Be patient some times it takes a min or so for it to reboot. Also try rebooting device with it plugged in to charger if it doesn't reboot unplugged.
I hope most of you know this...but from working at an Apple store (I no longer work at apple) it's amazing how many people don't.