I have had a simliar problem before, a temporary fix for me was to disable automatic update of date and time, then one day I re-enable it and all works fine... Where you change the time click on the "Internet Time" tab, and then untick the "automatically synchronise...." box, or you could try using a different time server like time.nist.gov. Although it has just occured to me that the computers are probably set to the wrong time zone, again in the window where you change the time, click on the time zone tab, and check it is set accordingly. When CMOS batteries go (in my experience) they just go and the clock will just reset to 00:00 everytime you turn it off, so unless you turn the PC's on at 7pm everyday, I find it unlikely that this is the problem and it would also be quite coincidental that it would do it on two PC's, also if this was the case you would likely get a prompt when you first turn the PC on warning you of this and usually saying "Defaults Loaded, Press F1 to Continue", but nevertheless (i think that is a word) it is still a possibility.

Cheers

James