IPod Not Recognised!

Hi there...

My iPod is refusing to be recognised on any computer. I've tried the school computers and my home computers. I have two cords, so I know it's not them. I have a wall charger, and it won't let me charge via that either. The only way I can charge it is via my Mum's docking station. When I plug it in to any computer, it says usb device not recognised. I have had the rare occasion last week where a computer at school allowed me to connect it. I just want to add 4 songs and be able to listen to them! Please help!