I have never recover the password from a stack of switches before but you will find the password recovery procedures for most/all Cisco equipment at this link http://www.cisco.com/warp/public/474/index.shtml
You need direct access to that switch and need to recycle the switch and hold down the botton in front that should be on the left hand side of the switch as the device is powered back up. once up, you will need to
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: