Read and follow these Apple Knowledgebase guides in the order shown, to help determine what the cause might be. If nothing helps, please post a new question with your findings, explain the troubleshooting steps you took and their results, and be sure to include your system information (e.g. OS X 10.6.8 and MacBookAir3,1).
General purpose Mac troubleshooting guide: Isolating issues in Mac OS X
Identifying resource hogs and other tips: Runaway applications can shorten battery runtime
Creating a temporary account to isolate user-specific problems: Isolating an issue by using another user account
Safe Mode or "Safe Boot" is a troubleshooting mode that bypasses all third party system extensions and loads only required system components.
Read about it: Starting up in Safe Mode
An SMC Reset might be justified, in the event you still experience inexplicably slow system performance.
Reset the SMC, then test your MacBook Air again.
Before Resetting the SMC
Try each of the following steps in this order before you reset the SMC. Test the issue after completing each troubleshooting step to determine if the issue still occurs.
- Press Command + Option + Escape to force quit any application that is not responding.
- Put your Mac to sleep by choosing the Apple () menu from the upper-left menu bar and then choosing Sleep. Wake the computer after it has gone to sleep.
- Restart your Mac by choosing the Apple () menu from the upper-left menu bar and then choosing Restart.
- Shut down your Mac by choosing the Apple () menu from the upper-left menu bar and then choosing Shut Down.
Resetting the SMC on portables with a battery you should not remove on your own
- Shut down the computer.
- Plug in the MagSafe power adapter to a power source, connecting it to the Mac if it's not already connected.
- On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
- Release all the keys and the power button at the same time.
- Press the power button to turn on the computer.