Server attempts reboot or shutdown, but can't

Question

I've been having a problem with a G4 Xserver. It had been intermittent (every couple of months) for a while, but it's been crashing multiple times a day recently.
I'm on 10.2.8, running AFS and FTP, with Netinfo for login. I have about 23 users, and it's rare for many of them to be on at any given time. I do have Retrospect client installed, and Timbuktu.
When it stops responding, I usually see the spinning daisy, as though the machine is shutting down or rebooting. Once or twice, I have seen the solid blue screen. The activity lights on the front panel are pegged at the top end.
Usually I get a run of several of these, then it stops. The first one has always had software update showing, which may be coincidence. This time, it's been going on for a week, and I need to get a resolution.
Crash logs and panic logs show nothing. Watchdog shows the restart process, but nothing for why the activity level pegged and it tried to restart. Automatic reboot is enabled in case of a freeze. Sample of watchdog log:
#Start-Date: 2005-09-20 09:59:41 AKDT
#Fields: date time s-comment
2005-09-20 09:59:41 AKDT     Started child "/usr/sbin/PasswordService" as pid 308.
2005-09-20 09:59:41 AKDT     Started child "/usr/sbin/sambadmind" as pid 309.
2005-09-20 09:59:41 AKDT     Started child "/usr/sbin/PrintServiceMonitor" as pid 310.
2005-09-20 09:59:41 AKDT     Started child "/usr/sbin/hwmond" as pid 311.
2005-09-20 09:59:41 AKDT     Started child "/usr/sbin/serversettingsd" as pid 312.
2005-09-20 09:59:41 AKDT     Started child "/usr/sbin/MacintoshManagementServer" as pid 313.
2005-09-20 09:59:41 AKDT     Automatic reboot timer enabled.
#Start-Date: 2005-09-20 11:55:08 AKDT
#Fields: date time s-comment
2005-09-20 11:55:08 AKDT     Started child "/usr/sbin/PasswordService" as pid 309.
2005-09-20 11:55:08 AKDT     Started child "/usr/sbin/sambadmind" as pid 310.
2005-09-20 11:55:08 AKDT     Started child "/usr/sbin/PrintServiceMonitor" as pid 311.
2005-09-20 11:55:08 AKDT     Started child "/usr/sbin/hwmond" as pid 312.
2005-09-20 11:55:08 AKDT     Started child "/usr/sbin/serversettingsd" as pid 313.
2005-09-20 11:55:08 AKDT     Started child "/usr/sbin/MacintoshManagementServer" as pid 314.
2005-09-20 11:55:08 AKDT     Automatic reboot timer enabled.
2005-09-20 11:57:27 AKDT     Re-reading config file.
2005-09-20 11:57:27 AKDT     Reaped child process 314 ("/usr/sbin/MacintoshManagementServer"); quit with exit status 0.
2005-09-20 12:06:01 AKDT     Re-reading config file.
2005-09-20 12:06:01 AKDT     Started child "/usr/sbin/MacintoshManagementServer" as pid 530.
I have done some looking around the web, and I hear of others having problems due to hardware issues (UPS, and so on). I will be replacing the battery tomorrow, and I'm considering resetting the PMU. Another other ideas?
My usual process is to run fsck and repair permissions. This usually does the trick, but not this time.
Thanks in advance!
Anne

Answer 1

I replaced the battery a week and a half ago, and it was up for over a week. After a couple of crashes after that, I started leaving the server closet door open, and that has kept it up for a couple of days. So far, so good.
I don't have a UPS. I did hear from someone in the neighborhood about a power outage one particular evening, but that's it.
The screen is used for 3 different machines, and is turned off or disconnected most of the time, so no screen saver. The only energy save options that are enabled are to restart after a power outage or freeze. It doesn't sleep.
I have heard, on the osx server list, about software update hanging computers, and, separately, about the PMU forcing a restart (instigated by restart when system hangs being checked). None of the exact details (hardward, OS, logs) are identical to my situation.
The next time it crashes, I'll uncheck restarting after a freeze or power outage.
Oh, there's a second machine right below it (slot-loading Xserver, same OS, does web server and moodle), and it has no problems. I keep thinking it is most likely some hardware issue (the jet-engine fans, maybe).
Thanks for the idea!
Something else that I tried, although it didn't give me anything useful:
I left process viewer running, but shut off the monitor. When it tried to restart, I could see the last view of process viewer under the spinning daisy wheel. Which showed process viewer as the highest CPU using item, at 2.7%. Although it was refreshing every 3 seconds and could have been outdated information by then, it was worth a try.