iPod not recognized by iTunes

My iPod is not recognized when by iTunes when I connect it to my iMac. I get the following message from iTunes. The iPod is showing in the system information under the USB.

"iTunes could not connect to the iPod touch “Gary Davison’s iPod” because an invalid response was received from the device."

There is nothing showing on the iPod. I have done all of the troubleshooting tips and still no connection