Have you tried booting safe mode?
To start up into Safe Mode press the power button and immediately after you hear the startup tone, press and hold the Shift key.
Note: The Shift key should be held as soon as possible after the startup tone but not before.
Release the Shift key when you see the screen with the gray Apple and progress indicator (looks like a spinning gear).
After startup, the words “Safe Boot” appear in red letters under the Apple logo on the Mac OS X login screen.
Note: The Safe Boot startup process takes longer than a normal startup. It can be quite long (several minutes) depending on the amount of time it takes to check and repair the directory (if needed).
To exit Safe Mode, restart the computer normally, without holding down any keys during startup.
After restart, hold down the Command-Option-P-R keys until you hear the startup chime at least one additional time after the initial startup chime.
1. If the MacBook Air is on, turn it off.
2. Connect the power adapter to a working power source.
3. Press (left) Shift-Control-Option along with the power button once. Note: Only use the keys on the left side of the keyboard.
4. Wait 5 seconds and press the power button to start the MacBook Air.
Caution: Reset the SMC only when the MacBook Air has been properly shut down. This prevents file system corruption.
Note: The power adapter is not required to reset the SMC, it may be necessary if the battery needs charging, or the MacBook Air has been off for a long time.