Workbook Exist

I run a workbook an I want to save it by it's date. In Simple word :
If the workbook did'nt exist save it, or it's already exist.

Sub SaveWorkbook()
Dim strFile As String
Dim FileName As String
Dim year As String
FileName = "Sales"
year = Sheets("Values"). Range("G2").Value
strFile = FileName & year ' For Example: Sales2007
ChDir "C:Sales"
If Dir(strFile) = "" Then
ActiveWorkbook.SaveAs FileName:=strFile, FileFormat:=xlNormal
Else
' Don't Accept saving and exit sub.
MsgBox "File already exist " & strFile, vbInformation
Exit Sub
End If
End Sub