Time resets into 24-hour time (and wrong time) on coldboot

My cousin's system basics:
Athlon XP 2000+
Windows XP Pro
McAfee VirusScan 8 (updated weekly)
ZoneAlarm Pro (newest version)
SpyBot Search & Destroy 1.3 (updated weekly)
Obnoxiously slow 56K dial-up connection

When we turn on the computer from a cold boot (not just a reboot), the time is reset to a random time, and is switched to 24-hour time. Every time I boot up the computer, I correct the time by double-clicking the clock and fixing the time, and I have even turned on Internet time sunchronization option. Then I change the format back to 12-hour time at "Control Panel -> Regional and Language Options ". In case the clock battery on the motherboard was dead, I even replaced it.

McAfee and SpyBot S&D are not turning up any issues.

The situation repeats under the following circumstances:
Cold boot into normal mode
Cold boot into safe mode

The situation doesn't repeat under the following circumstances:
Warm reboot into normal mode after I corrected the time
Warm reboot into safe mode after I corrected the time
Warm reboot into normal mode if I don't correct the time (continues where it left off)
Warm reboot into safe mode if I don't correct the time (continues where it left off)


If this was caused by a virus or other issue at startup, it would also occur in warm reboots, wouldn't it?

My cousins have a bad habit of turning off the computer at the surge suppressor. The situation even occurs regardless of whether or not the surge suppressor is turned off while the computer is turned off.

The tower has plenty of ventilation: 2 case fans, the processor fan assembly and the power supply fan. Also, there is plenty of room around the case for it to breathe.


What is happening here?

 

Couple of things to try...
Reset the BIOS to the default settings. Better still reset the CMOS. Check the motherboard documentation or remove the button battery for a few minites. Sometimes it's suggested to short the battery terminals for a few seconds after removal to accelerate the clear.

Replace the CMOS battery.

 

Sorry, it was the CMOS battery that I replaced. I did short the terminals before placing the new battery, and left it without a battery for about 5 minutes as per the motherboard documentation.

What is causing the randomness in time, and why does it default to 24-hour time?

 

Did you remember to set the date and time in the CMOS?

 

Yes, on the first boot after I replaced the CMOS battery.

You did, however, remind me of something odd.
After I replaced the CMOS battery, even during a cold boot, if I enter the CMOS, the date and time are correct.
It isn't until Windows booted that the time/date was wrong.

Any further suggestions?

 

start -> run -> eventvwr.msc and click OK.

Check both system and application event logs for errors that look like they might be related.

If you find one or more that you want examined, open the event, click the icon below the up/down arrows (places a text copy in the clipboard) and paste the information here.