I have an Compaq Presario S400NX running XP sp2.  The clock on this
computer is constantly drifting both when it is on and off away from
the correct time, sometimes by days.  Any idea what could be causing
this.  I did the sp2 upgrade around the same time as a RAM upgrade,
usb 2.0 ubgrade, and wireless card upgrade so I am not sure if any of
these have anything to do with the problem.

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Clarification of Question by ches3-ga on 05 Jan 2005 07:07 PST

So far I have tried,

Disabling my antivirus
Turning off the sync
Updating my BIOS
All permutations of these solutions.

The clock still drifts.

Possible causes:

A Winmodem
Your Anti Virus software
Problems with IDE drivers

Possible incompatibilities between the chipset and the hardware and the drivers.

Most probable it is the AV software. Turn it off and see what happens to the time.

You may also want to have your clock synchronize on a regular basis. 
To do this, double click your clock on the taskbar, then go to the
"Internet Time" tab and use the tools provided.

Source: http://www.microsoft.com/windowsxp/home/using/productdoc/en/default.asp?url=/windowsxp/home/using/productdoc/en/windows_date_IT_overview.asp

synchronizing on windows xp has its issues so as such i would say
disable it. Double click on your time that shows on the lower right
hand corener on your screen. Click the internet internet time tab
which is the 3rd one over then uncheak the box on the screen. Mine
drifted when i first got winxp and by turning off the synchronize it
quit losing time.

You might also want to try and update the BIOS on the computer.  I'm
pretty sure the OS gets the time from the system clock, which is
beyond the reach of any OS patch.  On the Compaq site there is a bios
update listed (<a href="http://h10025.www1.hp.com/ewfrf/wc/softwareList?lc=en&lang=en&cc=us&dlc=en&product=329399&os=228">here</a>),
although it does not list it as fixing the system clock.  It's
possible that there have been multiple revisions of the BIOS, and that
this is just the last revision, with an earlier revision containing
the fix.

Has this only been occuring since you installed service pack 2? If it
is possible that this has been occuring before then, it could be a
simple problem like your CMOS battery no longer keeping a charge. A
computer depends on the CMOS batter whenever power is removed from the
computer (which can be done by pulling the plug or flipping the switch
on the back of the power supply). Try opening up the case and taking
out a batter about 1in in size. They are cheap to replace and could
fix your problem.
If this does not work, there is likely a software problem. From there,
it is problem a communication problem between Windows and the
motherboard on your computer. You may want to try updating the BIOS on
the computer. Information on that can be recieved here:
http://h10025.www1.hp.com/ewfrf/wc/document?dlc=en&lc=en&product=329399&os=228&lang=en&cc=us&docname=c00007682

if it drifts from BIOS you may want to replace the battery on the
motherbord, if not go with the microsoft sync

So far I have tried,

Disabling my antivirus
Turning off the sync
Updating my BIOS
All permutations of these solutions.

The clock still drifts.

I will try to change the battery but I am not sure why this would
affect the time when it is plugged in.

The computer's internal clock only runs on the battery.  It does not
draw power from your AC source in most cases.  Therefore, a battery
that is malfunctioning would cause the clock to drift.

Also, if changing the battery doesn't help, check the contacts for the
battery.  Sometimes, if the batter is improperly seated or there is
corrosion on the contacts, the battery will work intermittently, which
would explain why sometimes it's behind and sometimes it's ahead.