why wont my ipod wont charge and itunes doesnt come up either?

i connect my ipod to my computer and it has the charging battery in the corner(where it shows how much battery the iopd has left) and i turn it off but doesnt show the charging sign.
when i connect it iTunes doesnt come up and even if i click on iTunes from the Start thing at the bottom it still doesnt come up
what should i do I NEED MY IPOD!!!