iPod has started buzzing and will not turn on

A magnet, if strong enough and close enough, can affect the iPod's hard drive. After removing the magnet from close proximity to iPod, does the iPod still "buzz" when you try to start it up? Try doing a Reset (restart) on the iPod

Learn how to reset your iPod - Apple Support (see section iPod with a click wheel)

Although I believe Kenichi has the better answer here, I sense that buzzing has more to do with power, as in incorrect voltage or amperage. Hard drive issues are identified more through clicking or grinding. Just a thought...

Also, buzzing, being less ominous than clicking or grinding, may lend itself toward the "slapping" of the iPod as a possible remedy, as described in previous posts here.