VBA Excel - COUNT, AVG, & MIN with textboxes

try this:

Option Explicit

Private Sub CommandButton1_Click()
    Dim ctrl As Control
    Dim sum As Long, avg As Double, count As Long, min As Long, max As Long
    min = 2147483647
    For Each ctrl In Me.Controls
        If TypeName(ctrl) = "TextBox" And Left(ctrl.Name, 3) = "txt" Then
            If IsNumeric(ctrl.Value) Then
                If ctrl.Value > 0 Then
                    count = count + 1
                    sum = sum + ctrl.Value
                    If max < ctrl.Value Then max = ctrl.Value
                    If min > ctrl.Value Then min = ctrl.Value
                End If
            End If
        End If
    Next ctrl
    If count = 0 Then MsgBox "Count = 0": Exit Sub
    avg = sum / count
    MsgBox "Sum = " & sum & vbLf & _
           "Count = " & count & vbLf & _
           "Avg = " & avg & vbLf & _
           "Min = " & min & vbLf & _
           "Max = " & max
End Sub