Hi Francis,
Usually the firewall boots with the the first application image that it finds in internal flash memory.
Try the following:
>Set the boot variable as:
hostname(config)# boot system url
url being:
{flash:/ | disk0:/ | disk1:/}[path/]filename
>Save the configuration:
hostname(config)# wr mem
>Now confirm that the boot image has been set:
show bootvar
Once done, reload the ASA and check if it is still going to the rommon mode.
Regards,
Shrinkhala