I just purchased a TT 720 last week. wanted to find out more about it, I searched around and found this forum. I am no expert. But I usually use Linux and have tried various things try to help me not have to bootup windows I noticed somethings that could help troubleshooting your problem....

1) when in the cradle do you see the green charging light?
2) when in the cradle and you see the green charging light turn theunit on it will ask you if you want to connect to the computer.answer yes the tom tom soft ware will then open on your computer. On Windows I noticed the TomTom logo was there but the program only opens when you tell the unit yes I want to connect
3) If answer to 1 is yes and 2 is no then makesure you are connected directly to the USB on the computer and nota USB HUB. I noticed if I plug it in andopen the program manually it will not regognize tthe unit ifit'spluggedintoa Hub.

If theanswer to 1 is no then it probablyis your cable
Hope that helps