Private Sub LoadSC_CDKeys()
  
Dim SCCDKey As String
Open App.Path & "\CD Keys\StarCraft.txt" For Input As #12
Do Until EOF(12)
Line Input #12, SCCDKey

End Sub

Option Explicit

Private Sub Command1_Click()
   'I'm passing the combo box so its name
   'doesn't need to be hard coded in the LoadSC_CDKeys sub
   Call LoadSC_CDKeys(Combo1)
End Sub

Private Sub LoadSC_CDKeys(TheCombo As ComboBox)
   Dim iFile As Integer
   Dim sCDKeys() As String
   Dim iItem As Integer
  
   'Instead of hardcoding a file number (12 in your case)
   'use Freefile to ask VB which numbers are available
   iFile = FreeFile
  
   'Notice I've changed your path, so I can test the code
   Open "C:\Temp\StarCraft.txt" For Input As iFile
  
   'Read the entire file and break it all up into
   'an array in one line of code
   sCDKeys = Split(Input$(LOF(iFile), iFile), vbCrLf)
  
   'Close the file
   Close iFile

   'Now, fill the combo and get outta here
   With TheCombo
      .Clear 'get rid of anything currently loaded
      'Loop thru the array, adding as we go
      For iItem = 0 To UBound(sCDKeys)
         If Len(sCDKeys(iItem)) > 0 Then 'no blanks allowed
            .AddItem sCDKeys(iItem)
         End If
      Next
      
      'Now, select the first item in the combo
      If .ListCount > 0 Then
         .ListIndex = 0
      End If
      
   End With

End Sub