for answering the question we need some information from your side look below :
operating system u are using.
hardware presently using with make and model .( external or internal device)
do u hace proper driver or not. if u have do u tried to reinstall it. if reinstalled what error message you are getting when trying to use the device.
and if you are using windows xp and above the first and easy thing you can do to resolve the issue is to use system restore .
if u need help feel free to ask