Our Sun computer was shutdown using shutdown -y -i5. During that
process we believe the power was turned off a bit prematurely.
Possibly, due to that when
the power is turned on again, the boot gets stuck at the step where the message
is 
setting default IPV4 interface for multicase: add net...

Though we are able to telnet to the computer and use it, we are unable
to see the clean prompt at the terminal connected to the Sun computer
itself.

I believe the next message should have been syslog service starting. There are
couple of more messages before we get the prompt. 

Do you know how this can be fixed? Thank you.

I would suggest running a fsck next time you bring the system.

boot in single use mode with 
ok boot -s

once you login there as a root.
#fsck -y /
perform the fsck for rest of the file systems you load at that time.
once they are done you can exit to the shell and it will boot up to multiuser mode.