When it freezes, does it start up if you disconnect the USB connection, or do you have to manually shut it down ?
My original 910 would often freeze my HP desktop, and if I did anything other then an immediate manual shut-down - it would sometimes do nasty things. I learned about recovering corrupted config files thanks to TomTom, and it finally crashed my computer motherboard. The unit itself finally quit while it was trying to connect to the repaired computer, so I got a refurb replacement from TomTom.
A technician (non-TomTom) thinks the device may have had a non-conforming USB connection circut that did not operate within the universal USB standards (ie, too high a voltage, etc.) and this may have taken the motherboard down. He suggested (after-the fact-unfortunately) that possibly putting an external USB hub between the TomTom and the computer may have prevented this.
You might give it a try. I hope your 910 is not going to take your laptop down like it did my desktop, as you cannot so easily replace the board. If it does go down and is under warantee, don't even mention the TomTom to the Laptop tech if the TomTom takes it down.
Good luck