need help correcting a macro-run-time erro 6 - overflow

Dear Excel Expert,

I created the following macro to run on a selected range, but if I select for example five cells in a column the macro does not stop at the fifth selection but continues to the very end of the list. I arbitrarily set the do until to .1 because I did not want the "do loop" to stop the macro but rather the other loop to stop it. I think this might be the problem though. And sometimes the macro doesn't run at all but gives me a Run-Time error - 6 - overflow.

Please help. Thanks Andrew

Sub Test8()
'
' Test8 Macro
' Macro recorded 4/25/2013 by .
'
' Keyboard Shortcut: Ctrl+Shift+Z
'
'This part is from "Variable Range and Input box" located in the folder
'Running a Macro on range(this is the folders approx. name)
    
    Dim myRange As Range
 
    Set myRange = Application.InputBox(Prompt:= _
        "Please Select a Range", _
        Title:="InputBox Method", Type:=8)
 
    If myRange Is Nothing Then
        ' Range is blank
    Else
        myRange.Select
    End If
    
  'The following is the loop part. This is from, "Create a loop". This is
  'document with the accompaning excel wk with multiple loops.
  
  ' This loop repeats a fixed number of times getting its reference from elsewhere
    Dim i As Integer
    Dim intRowCount As Integer
    intRowCount = myRange.CurrentRegion.Rows.Count
    For i = 1 To intRowCount
    
    'The nested part is a loop to perform the macro. It is also in the
    'document, "Create a loop" but it is not the same author. It is a
    'separate author.
    
'Here is my macro to format the cell
'Print ActiveCell.Characters.Count
With ActiveCell.Characters(1).Font 'counts 1 character over
'from the left, then seclects that cell and the next cell
.Color = RGB(0, 0, 0) ' black
End With

    'Print ActiveCell.Characters.Count
With ActiveCell.Characters(2).Font 'counts 2 characters from left
' to right and then below it is colored.
.Color = RGB(0, 0, 255)
End With
    
    With Selection.Interior
        .ColorIndex = 8
        .Pattern = xlSolid
        .PatternColorIndex = xlAutomatic
    End With
      
    ActiveCell.Offset(1, 0).Select
       
   Next i 'This is end part of the loop


End Sub

the best calculation for the last row used is

introwcount=range("A"&rows.count).end(xlup).row

selecting a column that is continuously filled up until the end.