why does my ipod classic (80gb) connect for a few seconds then disconnect?

I have a ipod classic 80gb, granted its old, but it has a big memory so I can store my whole collection. Anyway, when I connect it to my PC (with windows 8.1) it will connect for a few seconds then disconnect. It will sometimes start to sync, but then disconnect after a few seconds. My computer is pretty new, Acer Aspire V5. I have tried reinstalling itunes, a new cable to connect it, different usb ports(2) and with and without the pc plugged into the mains, which is when it starts to sync for a brief second. Has anyone else had the same problem??