Vista - CONTROL PANEL OPTION TO OPEN FOLDERS WILL NOT OPEN_NOT ASSOCIATED?

I am having a problem with 2 of the three computers I am currently running
Vista Ultimate on.

2 of them, when I go tot the control panel and try and open the folders icon
in the classic view produces an error message that states that it is not
associated and to go to associations to fix it.

I went there and can not for the life of me fiqure this out. Nor do I have
any idea how this might have happened.

would appreciate anyone helping me fiqure out this little probelm...
I wondered if there was a way in Vista to either repair or to restore all
defaulkts if one choose to do that?

many thanks
john