iPad Not connecting to MacBook Air via USB
Open up Diagnostic tests, by clicking About MY Mac, and run the test. This will also test which USB ports on the Mac are working. If your iPad charges then the power is working on the USB port, but the data transfer is probably not.
The iPad itself could also has a fault, and to test this, use a different device and see if that shows up on the device. Also try reseting the iPad to factory default (backup first) or just rebooting could work as well. If not of those work, try using a different USB port, or try using a different computer.