Why can't my itunes recognise my iPod?

Why can't my itunes recognise my iPod?
when I connect my ipod to my pc, my pc can only charge it but my itunes can't see it and I can't see it as a hard drive. what should I do?

ANSWERS:

Some iPods will charge using a firewire cable but they can't be read. Try using a high quality USB hook up for reading.