|What about the date? If it's the cmos battery the date usually reverts to midnight (00:00) on the bios creation date--which is usualliy about the time the computer was built or the bios upgraded. 1:00 pm is kind of an odd time for it to reset to especially if the date is correct.|
You can set the date and time both in bios setup and in windows. Be sure to save the settings.
I doubt it's a factor but for XP it's probably best to uncheck the box that says 'automatically adjust clock for daylight saving changes' in the 'adjust date and time' box as I don't think XP has any updates for the recent date changes. Also you might try enabling/disabling the 'synchronizing with internet time' option and see if that makes a difference.