plug it out and plug it back in.
there is an existing problem if you try to connect a PS3-controller to a 64 bit windows: the usb-drivers get corrupted. solution: reinstall the drivers.
this can be tricky if you cant use a mouse and keyboard, to solve that get a ps/2-adapter to connect at least the keyboard to your pc (if you're lucky, you still have a ps-2 connection for mouse too)http://www.newegg.com/Product/Product.aspx?Item=N82E16812200272&cm_re=ps-2-_-12-200-272-_-Product
(an example of an adapter, search it in your closest shop)