I never experienced this Linda, but I did do some research on then internet. In this case I assume that you have Windows, but most solutions could work for MAC also (using other tools).
a) make sure that your preference file is not read-only
b) check your disk; run a scandisk (right click on drive/properties/tools)
c) on windows 2000/XP it might be possible that your file or the locations of your file has the wrong user permissions.
A short quote from a newsgroup article;
"The odds are you have your main startup drive permissions set to read only so that Photoshop is unable to actually save the preferences. check the OS X site at Apple for a thing called permissions fixer (or something like that). Some recent software installers are re-setting the permissions to read only without warning the user."
This is all what I can come up with at the moment.
Good luck