device manager

itunes and windows dont recognise my ipod. am setting it up on new computer, worked fine on last one. have tried reinstalling itunes again. does not work. noticed in device manager under usb that with apple mobile device usb driver it has an exclamation mark on it and when click on it it says 'Windows cannot verify the digital signature for the drivers required for this device. A recent hardware or software change might have installed a file that is signed incorrectly or damaged, or that might be malicious software from an unknown source. (Code 52)

how do i fix this