It is best to connect to the ASA console port with your laptop/computer and view the logs while it boots. Feel free to post the output here when it is captured.
It would be nice if we can know the version of ASA code running, Do you have any IPS Module in the kit installed?
is this new, or working one, Due to loss of power? this slow causing?
as suggested other post, good to connect console and post full boot process, how long you thinking this boot process takes?