How do I get a cell to not change value if the IF statement returns FALSE?

eg.

I have a drop down list that makes reference to a set of names and another drop down list that makes reference to a set of weeks. When I select a specific name and week from the drop down lists, they will apply an entered value into the intersecting cell of the selected name and week. However, I don't want the value to change when I select a different name or week unless the name and week are the correct ones.