Problem with root account on old SVR4 server

I have an old Unisys server (SMP-61000) running SVR4 Unixware version 1.4.2. I had some trouble with the internal disk drives and could not get the system to boot up last week. I took the server apart and checked hardware scsi connections and whatnot, and when I put it all back together it booted up normally. When I tried to log into the console as root, however, I get an "invalid ID" message. I can log in as any other user on the system, but not root. There are no other root-equivalent users. So basically, the system is running normally, but I could not shut it down properly if I wanted to. Obviously, something was corrupted when I had the original problem. Does anyone have any idea of how I can fix this problem when I can't do anything that requires supervisor or root access?

It seems to me, the /etc/passwd and (or if you have) /etc/shadow entry
for user root (uid=0) is corrupted.
i don't understand you are able to boot, for this the uid 0 is required...
on solaris or bsd, i boot from cd then start a single user shell, mount the root
partition and check/fix those files.