Might be a simple fix - swap USB cables
I just had the same problem, PC wouldn't recognize any device was connected, and TomTom didn't see it was connected (but was drawing power from the PC since the green power light went on). The PC would flash, but no "new hardware" window, no USB connected and no deviceturning up in the Device Manager disk drives list (which is involved in the solution linked in the suggestion above).
I found my solution by accident - I used a different USB cable. I have USB cables everywhere in here, so I used the first one at hand. Later, I thoughtlessly left that cable on the counter after a frustrated trip for more caffeine, so when I got back I used a different cable, and it connected. Tested two other USB cables, and only one of the three allowed my PC to see the device. No idea why the TomTom is fussier that way than other hardware.
I do realize (having had TomToms before) that most times the problems getting the PC to recognize the device and vice versa is a lot more complex. But it probably won't hurt to try a different cable if you have spares on hand. You might get a nice surprise.
Good luck!
