Building new kernel help

[Darryl Hoar]

Greetings,
I have installed 5.1-release on a box that will ultimately be
a firewall for my home network.  Everything went fine.
When I modified the kernel (/usr/src/sys/i386/conf)
and remade the kernel (followed the /usr/share/docs
instructions) and rebooted, the system would start coming
up.  Get to the menu screen.  I'd choose 1, and it would
start showing the devices like normal, then reboot
(automatically).  Tried to boot single user, and the same
thing happens.

How do I boot the old kernel ?  I built the new one with the
/usr/sbin/config, make depend, make,make install sequence.

thanks,
Darryl