Won't restart after sitting several days: 3.3 minimal on a 170MB drive

["gjohnson" <gjohnson_(_at_)_molions_(_dot_)_com>]

     On two separate Dell Dimension XPS Pro200n computers , I performed a
minimal install of obsd 3.3 (not even comp) via LAN ftp.  The ethernet card
in each was a 3Com 3C905CX-TXM.  The computers were stock except for the
memory (48MB in one and 64MB in the other), the ethernet card (3Com
3C905CX-TXM in one; 3C905-TX in the other), the hard drive (170.6MB Western
Digital Caviar 1170 in each).  I partitioned each drive with 4MB of swap
and the remainder as /.
     Each machine started fine (it was last Monday, I believe).  I ssh'd
into each successfully, and commanded each to "halt".  I restarted each
without a problem.  I halted each machine a day after the installation and
let them sit until today (Sunday).  Now,  when I start each machine I
receive the message "Insert bootable media in the appropriate drive."
     I did the installation above to confirm this error.  To be more
precise, I had found this same exact error on the same machines when I had
installed obsd3.3 on them (exactly as above) about 4 weeks ago and
restarted them.