Search fails in Apple Mail -Solved -now can't delete post?

The search function is not responding in Apple Mail (10.9.5) Even if I enter a name of a sender (already in contacts) who's recent email is visible in the inbox there is no result. I'm typing correctly and none of my contact names will appear using search. As stated, I can SEE the sender's recent emails -but there is NO result if I perform a search. (I searched "sender" "any", all options in specific accounts and all accounts (I only have 2) It is important to be able to access this function! I'm afraid to delete "prefs" unless instructed

thanks