cannot boot, at mountroot> prompt

[Bob Collins]

I have a system running 5.0-RELEASE on an AMD 667Mhz processor with 256MB 
ram, Soyo mobo. Install was no trouble, and setup of X, KDE, MySQL, Apache 
went fine. I ran a setup of both xmms and mplayer as well. Then I went for 
an install of Webmin.

Once webmin was complete, I was running in KDE, I closed the term window 
and the machine rebooted immediately, no shutdown, nothing.

Question, does this sound like a bad drive, RAM, or perhaps my bad luck.
Second question, how can I address the mountroot> prompt?

Per the instructions at the prompt, I put in ufs:/dev/ad0s1a and hit the 
return key. The system then reboots.

Thanks
Bob