is your DHCP online after the power cut? setting "Keep AP setting" only means that the APs will continue to DHCP or Static IPs according to what is configured on them, it doesn't mean they will save the DHCP lease they got! In other words, the APs still need DHCP, if you turned it off, the APs will all come up with their default IP.
Also, check your switch configuration. On most switches you need to manually save the configuration after making changes (eg. 'copy running-configuration startup configuration' or 'write mem'). Many times this step is forgotten so the switch runs with the configuration in RAM, when the power fails, all the config is lost.