My iPod will will not sync or charge at all.

My ipod was working perfectly and left on for a long period in my car, tried to use it and it would not turn on, I tried to charge it and nothing, nor would it connect or sync with my laptop. I have tried all the resets and everything possible and nothing worked, so I bought a new battery, changed it and it came on with half power and worked perfectly except it still wont connect to my pc or charge, carried out the reset, put it in disk mode, I have run the diagnostics and nothing works, when running diagnostics it always said no usb cable connected, but it was connected all the time. Please help, what causes an ipod to just fail?