What Causes My Display Theme to Change?

[Guest Judy]

I have my display set to "Windows Classic" with a 'teal' background. . . . .

dull, I suppose, but I like it. But about once a week or so, when I turn the

computer on, the display has changed to "Windows XP". This never occurred

until about 6 months ago. Can anyone tell me what's it causing this, and/or

how to fix it. I know how to RESET it--but I'd like to know the way to keep

it from happening at all. Thank you for your help. Judy