Regarding balance not showing up, please refer to ThomasV post above.
Even with a good USB cable there can by some "funnies" with the communications between Trezor and Electrum, particularly if the Trezor is connected or disconnected while Electrum is running (this is on Windows 7). The solution when this happens is to unplug the Trezor, exit Electrum, wait 30 seconds or so, and then reconnect Trezor and restart Electrum.
I have no idea how to diagnose this problem is it doesn't happen often and I haven't been able to cause it to repeat predictably, nor do I know what diagnostic logs (if any) I should be looking at. For all I know it could just be an unrelated random system glitch on my Windows machine and not actually have anything to do with Trezor or Electrum.
I post this only so that if other people are experiencing similar problems some insight on this might be found that can lead to improvement. In the general scheme of computer and Bitcoin frustrations this is not a big issue, IMO.