Red cross on sd card on startup
You can not use a sd card from one TomTom and put it into another TomTom. The operating system on the card is coded for each individual TomTom device. First try doing a reset with the card installed on your dads TomTom. The reset hole is on the bottom of the TomTom marked reset Use a streightened paper clip, insert the paper clip into the hole until you feel a click then hold it in for 20 seconds. If that didn't work and you have a card reader insert your dads sd card into the reader and make a backup of the everything on the sd card. Just copy and paste everything on the card to a folder on the desktop you have created on your desktop. Next delete everything on the sd card EXCEPT the maps and ttgo.bif or ttgo.bak file. Now that you have made a backup and deleted everything on the sd card except for the maps and ttgo.bif or ttgo.bak open TomTom Home. TomTom Home should see your card and install the operating system back onto the sd card. If it doesn't you may have to insert the sd card back into your dads TomTom and connect it to the pc. It may take a few times of doing this to get the latest operating system back onto your dads TomTom. You can do the same for your TomTom, but you cannot use any thing bigger than a 2 gb sd card. Do not get sdhc cards they won't work. This will only put the operating system for your TomTom onto the sd card. When you have installed the operating system onto your device it will say "no maps found", you will have to buy the map from TomTom..