Amy Winehouse

why wont my computer recognize my usb phone?

I have a cell phone called a Motorola Rival, and i want to get all my pictures and videos and all that on my memory card to my computer. So i plug it in, and the phone says unathorized charger, but it starts charging. my computer does nothing. show absolutley no evidence of the device being plugged in. so i go to menu, tools, USB mass storage, to see if i have to go into USB mode like you do on a PSP. so i press continue and it says you are still not connected to a PC. and i dont know what to do. can someone please help?