Have you put the start and stop * characters around the barcode? If you want to create a Code 39 barcode for the string "ABCDE" then you need to type "*ABCDE*".
IMPORTANT: MS Word has a feature that automatically converts any text surrounded by * characters into bold. If this feature is enabled then your barcodes will not work. To disable this feature you will have to select Autoformat from the Tools menu and un-tick the "*Bold* and _Italic_ with real formatting" option on the "Autoformat as you type" tab.
