whw

I have had my most recent computer six months. I set my own desktop theme and have a "Theme" file that restores it. Infrequently I noticed that on starting up the computer the theme changed to the typical blue, red and green Windows XP style, although all my other settings were retained. I could restore my own theme with no problem. In the last week, however, this has happened three times, twice on one day. Again, I can restore my own theme easily but wonder if there is some problem that will get worse. I have used Windows XP Home on my old computer and my laptop and never experienced this irritating problem before. Can anyone help?