Format Data Type of Selected Cells in a Loop

I'm trying to change the data type of the selected cells using VBA and my current code is not working. I'm looping through multiple Excel files in a directory but it seems like the current code either doesn't open the workbook or save the change in the end.

I want to open each Excel file, change the data type of the two selected cell, and save the change. Here's the code I have now:

Sub Formatting()
Dim MyFolder As String, MyFile As String


MyFolder = "C:\Users\Documents\Files"
Application.ScreenUpdating = False

MyFile = Dir(MyFolder)

Do While MyFile <> ""
    Workbooks.Open fileName:=MyFolder & "\" & MyFile

    Range("G4").NumberFormat = "0.00"
    Range("E4").NumberFormat = "m/d/yyyy"

    Workbooks(MyFile).Save
    MyFile = Dir
Loop

Application.ScreenUpdating = True

End Sub

Save the workbook object into a variable, and then use that with the ActiveSheet.Range.

Dim wb As Workbook
Do While MyFile <> ""

    Debug.Print MyFolder & "\" & MyFile

    Set wb = Workbooks.Open(FileName:=MyFolder & "\" & MyFile)
    wb.Activesheet.Range("G4").NumberFormat = "0.00"
    wb.Activesheet.Range("E4").NumberFormat = "m/d/yyyy"
    wb.Close SaveChanges:=True
    MyFile = Dir
Loop

_{Note: if there is more than one sheet, whichever one is active will get the change. If there is a better way to identify the sheet, then use that instead of ActiveSheet.}