This is actually password recovery but bypass startup-config gives more meaning. Sometimes you can save your configuration and when you reboot it goes into setup mode.
http://www-tss.cisco.com/eservice/compass/common/activities/password_1700.htm
Cisco password recovery google keywords
Cool video from bryant advantage http://www.thebryantadvantage.com/CCNA640802CCENTConfigurationRegister.htm
Latest Cisco link to procedures for Cisco equipmenthttps://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_tech_note09186a00801746e6.shtml
Sat450's Weblog 