Try this

The only problem with this code is that it might sometimes not create Alphanumeric Strings...

You can put in an extra check to see if the string is an alphanumeric and then only store it in a cell... I am sure you will be able to do it... If you get stuck simply post and we will definitely help you...

Code:
Sub GenerateRandomString()
    '~~> This will generate a passwords 5 chars long and
    '~~> Store it to Cell A1 in Sheet1
    Sheets("Sheet1").Range("A1").Value = RandomString(5)
End Sub

Function RandomString(Lngth As Integer) As String
    Randomize
    
    Dim baseString As String
    
    baseString = "abcdefghijklmnopqrstuvwxyz"
    baseString = baseString & UCase(baseString) & "0123456789"

    Dim i As Long
    For i = 1 To Lngth
        RandomString = RandomString & Mid$(baseString, Int(Rnd() * Len(baseString) + 1), 1)
    Next
End Function