According to the support guys at Navman. Select the voices tab on the left hand side of the Navdesk front page. Your Sat Nav needs to be connected.
Once that is open on the left hand side is all the voices available in all the different languages. The right hand side shows the voices installed. As you have had them all deleted this side will be blank.
Go to the correct country for your needs and select the male or Female voice (or both) of your choice. Insert the Navdesk CD / Dvd into an available drive as this is where your selected voices are downloaded from. At the bottom of the page click the select button. Important note the CD ? Dvd is needed for this to work.