Your Select Case code is slightly awry. Basically what you are saying is that depending upon the length of txtWeek you want something to happen.
Now each case event is purely derived by the length of txtWweek. I will use pseudo code
Select Case Len(txtWeek)
'the length of txtWeek is one character long
Case 1: Action 1
'the maximum length of 2 characters gives
Case 2: Action 2
I think that you will realise that you cannot use a keypress event to trigger the Select Case as it will only ever contain the one character (or should!) perhaps Exit might work but seriously the best option is to discard the textbox in favour of the Listbox.