Checking If A Value Is Present In A Cell If So Changing To The Cell Below

Problem Designing "new customer" form, a textbox(forename) in the
form has the Control source of "B3" (an empty space in my Customer
database). When the form is run and the forname is typed in the box, it
fair enough appears in the Database sheet (in B3).
However, then when opening the form again and typing over the forename
just inserted it will ofcourse overwrite it (B3 is replaced). Any ideas how i can input
code into the sub linked to the textbox so that it checks the control
source and moves down if the source is empty(code checks B3 for text, moves to B4) then the next one (B4 is checked, moved to B5).


Dim topCel As Range, bottomCel As Range, _
sourceRange As Range, targetRange As Range
Set topCel = Range("B2")
Set bottomCel = Range("B65536").End(xlUp)
If topCel.Row > bottomCel.Row Then End
Set sourceRange = Range(topCel, bottomCel)
Set targetRange = Range("B3")