I want to stop the (part of the program that presents the) 'Egg Timer'
symbol when I run my macro.

If the user clicks on cell "b3" when it already contains a Part Number, I
want a message Box to appear. The following code does the trick, except that
the Egg Timer symbol appears until the OK button is clicked in the MsgBox.

If IsError(Range("B3").Value) = False Then GoTo DoubleClick
(If "True" code snipped)
DoubleClick:
Sheets("Main Page").Select
MsgBox "Part Number has already been assigned."
Range("B2").Select
Exit Sub

What am I missing?

Thanks.

Mike