What year is your MB Air and what version of OS X is installed?
You could try resetting the SMC and the PRAM. It won't hurt and it may solve the problem.
To reset the SMC: Make sure the Mac is plugged in to AC power. On the built-in keyboard, press and hold the Shift, Option, and Control keys on the left side and press the power button. Release all the keys at once, and then turn the Mac on normally.
To reset PRAM: Shut down your Mac, press the power button, and as soon as you hear the startup chime, hold down Command-Option-P-R. Keep holding down those keys until you hear a second startup chime. Then let go and allow your Mac to continue starting normally.
If neither helps, post back and provide the information about year and OS X version.
Lisa