If your iPod flashes off and won't turn on again, it's out of battery. Other reasons for flashing off include software glitches and corrupted files. Apple offers a number of steps to try to fix this type of problem. If they don't work, it's possible that your iPod is damaged or faulty, in which case Apple's one-year limited warranty should cover it.
If you see a low-battery message displayed and then the iPod flashes off, or in the case of an iPod Shuffle, a red light flashes and then the unit turns off, the iPod has shut down to preserve data. Plug in your iPod for a few hours to fully recharge its battery.
Audio files, video files and even apps can be corrupted. This doesn't necessarily mean they have a virus or a serious problem, just that they can't work correctly because of missing or incorrect data. If your iPod flashes off while playing the same song or game, delete that song or game and re-download or re-sync it.
One of the first steps Apple recommends for any minor iPod glitch is to turn the device off and on again. This gives the operating system a chance to reboot. IPod touch and Nano have a Sleep button. Hold it down for a couple of seconds to turn it off. For iPods with a click wheel, hold down the "Play" and "center" buttons for six to eight seconds until the Apple logo appears.
Doing a factory restore on your iPod is a last resort if other troubleshooting methods have failed. It won't damage your iPod, but it does wipe all your data and you'll have to re-sync afterward. Plug in your iPod and select it under "Devices" in iTunes. Click "Restore" and wait while the iPod is wiped and its operating system is reinstalled.