Microsoft Excel , Goal Seek function

Question

Hi, 

I am using the code below to find value on the target cells and  I want to set a condition that the target value obtained in cell (D66 )has to be (>= 0 ), same for ("D66"), ("D68") and ("D70").

1- How can I do that ? and how to add multiple constrains?  

2- and is it OK to use Goal Seek function to solve the value in one cell then use the calculated value into another cell where I set Goal Seek function as       well so I can run multiple Goal seek to do kind of loop to solve 2, 3, 4, 5 or even 6  equations in different cells with different conditions and they             might be related to each other in some how? 

the code is:

Private Sub Worksheet_Change(ByVal Target As Range)

Dim bSuccess As Boolean

    On Error Resume Next

    bSuccess = Range("C66").GoalSeek(0, Range("D66"))

    On Error GoTo 0

    If Not bSuccess Then

        MsgBox "Goal Seek Failed for Cell ""C7""!"

    End If

    On Error Resume Next

    bSuccess = Range("C68").GoalSeek(0, Range("D68"))

    On Error GoTo 0

    If Not bSuccess Then

        MsgBox "Goal Seek Failed for Cell ""DAfStb""!"

    End If

    On Error Resume Next

    bSuccess = Range("C70").GoalSeek(0, Range("D70"))

    On Error GoTo 0

    If Not bSuccess Then

        MsgBox "Goal Seek Failed for Cell ""EC2""!"

    End If

    On Error Resume Next

    bSuccess = Range("C72").GoalSeek(0, Range("D72"))

    On Error GoTo 0

    If Not bSuccess Then

        MsgBox "Goal Seek Failed for Cell ""DAfStb""!"

    End If

On Error Resume Next

    bSuccess = Range("C77").GoalSeek(0, Range("C38"))

    On Error GoTo 0

    If Not bSuccess Then

        MsgBox "Goal Seek Failed for Cell ""DAfStb""!"

    End If

    On Error Resume Next

    bSuccess = Range("C78").GoalSeek(0, Range("C37"))

    On Error GoTo 0

    If Not bSuccess Then

        MsgBox "Goal Seek Failed for Cell ""DAfStb""!"

    End If

End Sub

Answer 1

Well, basically any one can be run automatically and give the solution every time and satisfied the conditions!   

If you can help me to write that I would appreciated, because I am new user and really need that urgently.

regards

Answer 2

Please I need answer ASAP!!!!!!!

Regards all