Suddenly, my TF isn't passing any sound with the power on. Settings make no difference.
If I take the power lead out I get my guitar signal back.
Put the power lead back in and it passes signal for a few seconds until the TF wakes up, then it cuts the signal. The cut is accompanied by the single interal click sound I get using the update facility.
First try "Restoring Factory Settings" as described in the User Manual.
If this doesn't work, it sounds like a power supply problem. If you are using the supplied power supply you should contact email@example.com. If not, you should contact the power supply manufacturer.