Option for USB input disappeared

I have been recording old cassette tapes using a usb connection. I don’t know how, but I now only have “Built In Input” as an option. USB is no longer in the drop down list. I uninstalled Audacity and reinstalled the most current version and still have the same problem. I think I installed from dmg - not entirely sure. I am using Mac OS X 10.7.5

Thanks for any help!

Ensure that the USB device is connected and recognised by your computer before you launch Audacity.

Or click on the Transport menu and select Rescan Audio Devices.
– Bill