This doesn’t require a CD or anything just an internet connection. Restart the Air When you hear start up Chime hit (and hold) the Option button Goto Drive options… (something like that disk utility?) and under the advanced tab reformat your HD. Reinstall OS (this is available through this start up utility, it goes out on the  Full Article…

Taken from here: https://discussions.apple.com/message/20953957#20953957 Step One – Back up your data: A. If you have any Virtual PCs shut them down. They cannot be in their “fast saved” state. They must be shut down from inside Windows. B. Clone to an external drive using using Carbon Copy Cloner. 1. Open Carbon Copy Cloner. 2. Select the Source volume from  Full Article…