When I install the boot manager and try to boot FreeBSD for the first time, it just comes back with the boot manager prompt again.

Frequently Asked Questions for FreeBSD 2.X : Installation : When I install the boot manager and try to boot FreeBSD for the first time, it just comes back with the boot manager prompt again.
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3.9. When I install the boot manager and try to boot FreeBSD for the first time, it just comes back with the boot manager prompt again.

This is another symptom of the problem described in the preceding question. Your BIOS geometry and FreeBSD geometry settings do not agree! If your controller or BIOS supports cylinder translation (often marked as ``>1GB drive support''), try toggling its setting and reinstalling FreeBSD.