The
boot> prompt appears before the kernel is executed, you'll only see a
ddb> prompt after the kernel has loaded.. you can reboot the machine from ddb using "boot reboot" as documented in the
ddb(4) man page.
You haven't included output, simple stating "a kernel page fault" is not adequate.. and you'll need to be far more verbose when reporting the problem to the developers.
As was said, you can try disabling acpi (..although on newer systems, this isn't always a good idea), or try booting the single-processor kernel instead.
Reading on screen instructions is also a good thing to do, as they are displayed when the kernel panics.