As of the time of this writing, Google does not provide a USB driver (for Windows) for the Nexus 5. The usual link (http://developer.android.com/sdk/win-usb.html) shows Wind
Are you sure it's a driver problem? A device that isn't detected probably has a hardware or firmware problem. If it isn't detected, you won't hear the USB device detected chime. It might not be serious, e.g. some "USB" cables are really only charging cables. Try a USB cable that you know works for data, e.g. the one that came with the phone or one you use for connecting an external hard drive.