Did you try the specific instructions here: http://support.arubanetworks.com/Documentation/tabid/77/DMXModule/512/Command/Core_Download/Default.aspx?EntryId=1634
"Reset Button The reset button can be used to return the AP to factory default settings. To reset the AP: 1. Power off the AP. 2. Press and hold the reset button using a small, narrow object, such as a paperclip. 3. Power-on the AP without releasing the reset button. The system LED will flash within 5 seconds. 4. Release the reset button. The system LED will flash again within 15 seconds indicating that the reset is completed. The AP will now continue to boot with the factory default settings."
If that does not work, and you don't have a console cable, please contact TAC.