Find Next Function with two criteria Help

Try this...adding Application.ScreenUpdating = True and Application.ScreenUpdating = False like so...

Sub GoalSeek()
 Dim i As Long
 
 Application.ScreenUpdating = False
 For i = 5 To 75500
 If (Range("Z" & i) = 12 Or Range("Z" & i) = "") Then
 Else
 With Range("Z" & i)
 .GoalSeek Goal:=12, ChangingCell:=Range("X" & i)
 
 End With
 End If
 Next i
 Application.ScreenUpdating = True
 End Sub

It might help a little bit.
I have a question though, you have a If Then statement, but after the Then it goes straight to Else. Usually there is something in between.