I am kinda where you are thinking with this:
Private Sub Txtuser_Click()
Me.Txtuser = Environ("Username")
If (DLookup("TblALLUsers", " (userlogin) = '" & Me.Txtuser & "'")) Then
MsgBox "User needs added to data. Please contact the local CSM", vbOKOnly, "Login Info"
The logged in...