run macro with input msg based on cell input
 

I need help to run a macro with input msg when a date is entered into the
cell eg. date is input to cell M20 - input message "Budget received - do you
want to complete Budget Calculator" If "Yes" is selected then worksheet
"Budget Calc" is copied and renamed based on contents of cell A2 (I think I
have the renaming sorted thanks to previous posts). If "No" selected then
macro stops.
Any help would be appreciated.