Although iPods are one of the best engineered music players on the market, being electronic devices there is always the chance of component failure. That said, in our experience many iPod problems can be resolved by the following:

Reset
On iPods with a clickwheel, flick the hold button on and off then hold down the top and middle buttons of the wheel for 6 seconds or so. This should reset the iPod.

Reinstall iTunes
Always ensure you have the latest version of iTunes on your computer as Apple regularly update it to improve performance and eliminate known issues.

Restore
In iTunes use the 'Restore' function. This will erase your iPod completely before reinstalling its software and then your music.

For more details on these functions, please refer to the Apple troubleshooting guide.