Install 5.3 - Getting mountroot> prompt

[Scott]

I will really appreciate it of someone can help
me out.

I am installing 5.3 on a dual p3 server. I have
two 160 gig Seagate IDE drives on the first IDE
connector, and a CD rom on the 2nd IDE connector.
I have reinstalled several times with different
drive configurations and keep getting stuck at
the same place.

At boot, the normal countdown loader comes up and
it begins to boot. The boot message gets to this
drive section below and then stops at a
"mountroot>" prompt.

Begin copy ....... 

ad0: 152627MB <ST3160023A/8.01> [310101/16/63]
at ata0-master UDMA66 
ad1: 152627MB <ST3160023A/8.01> [310101/16/63] 
at ata0-master UDMA66 
acd0: <CDU5211/YYS2> at ata1-master PIO4

Manual root filesystem specification:
<fstype>:<device> Mount <device> using filesystem
<fstype> 
eg. usf:da0s1a
 ? List valid desk boot devices 
<empty line> Abort manual input

mountroot>

 ............ End copy

If I type: ufs:ad0s1a 
at that "mountroot>"
prompt, it will boot normally and as far as I can
tell, all is working like I would expect. I
suspected this may have something to do with my
fstab but it looks normal to me:

/dev/ad0s1b  none      swap  sw  0 0 
/dev/ad1s1b  none      swap  sw  0 0 
/dev/ad0s1a  /            ufs     rw 1 1 
/dev/ad1s1d  /backup  ufs      rw 2 2
/dev/ad0s1d  /tmp       ufs      rw  2 2 
/dev/acd0     /cdrom    cd9660  ro,noauto  0 0

Please let me know if I can provide more
information that will help you help me know
what to do to get it to automatically go on 
to boot ad0s1a.

Thanks much, 
Scott