drop down box

Every once in a while whenever I go to click on something a drop down box comes up with open etc for that program no matter what it is Safri or mail anything. click on open & it just brings up the drop down box again can't open anything. After a few min it will go back to normal. Is there a setting that I have wrong or something.

imac 20' 1Gb ram

just got it on Friday.

Thanks for the help. This is a great place for us newbie Mac users


Robin