Pop up question if data already exists

[fifusalir]

Hi

I have a excel sheet that users use to input data in to table.
The following data that user has to input is:
Column
B= Name
C= Quarter
D= Year
etc....

What I want is when user puts in a name, quarter and year and more information excel checks if following data(Name,Quarter and Year) already exists in the table it sends to.

Pops up with a question: "This information already exists want to override the data or cancel?"

And then ether the new data overrides the existing data or cancels the process.

With thanks
Arni.