Hi ibrahimaa,
You could use a 'Worksheet_SelectionChange' macro like the following in the relevant worksheet's code module:
Code:
Private Sub Worksheet_SelectionChange(ByVal Target As Excel.Range)
If Target.Address = "$A$3" Then
If Target.Value = 123 Then
Application.EnableEvents = False
'Call your other macro here
Application.EnableEvents = True
End If
End If
End Sub
In the above example, your macro will be called if cell A3 is selected and its value is 123. Note that merely selecting the cell when it has this value will be enough to trigger the macro. If you don't want that, you might prefer to use the 'Worksheet_Calculate' event. That event, though, won't be triggered by inputting anything into the cell unless that results in the worksheet re-calculating.
Code:
Private Sub Worksheet_Calculate()
If ActiveCell.Address = "$A$3" Then
If ActiveCell.Value = 123 Then
Application.EnableEvents = False
'Call your other macro here
Application.EnableEvents = True
End If
End If
End Sub
You'll note that, in both case, I've included some Application.EnableEvents lines. Depending on what you're doing you may or may not need these.