Why won't my Carminat TomTom SatNav display any maps since latest download?

I forgot to do the WRNO update prior to April 6th. I recently updated the SD card for my Carminat TomTom for a Renault Grand Scenic. The SD card downloaded the updates successfully from my laptop. I inserted the card back in the SatNav, turned it on and followed the instructions. Once it loaded ok I returned the SD card to the laptop as initially instructed and another small update was there. I did that update, returned the SD card into the SatNav and now all I get is a yellow box with an "egg-timer", the screen goes black and a line scrolls across the bottom of the screen and then returns to the yellow box/"egg-timer" and this goes on and on and on! How can I fix this? Please Help!!