only allowing data in 1 of 4 cells

Hi Folks,

As part of a project I am working on I need to get a user to select yes/no from a drop down list from 1 of 4 cells and prevent the other 3 from being modified once one has been changed to yes.

All 4 cells start as no and I need the user to pick one to chnage to yes but prevent more than 1 yes.

Is this possible?

To me this eems rather complex so thought the solution might be VB so posted it here. Please feel free to point me to the correct board if my assumption is wrong :-)

Cheers

J