What model do you have? 2, 3 or DUET?
What software or firmware are you using? Try downloading the latest release to see it everything works. If you are still trying to use firmware 15, it is no longer supported by Logitech.
There are a couple of common hardware failures. One is the connectors that join the daughter board to the main board on the SB2 and 3 comes loose. This will usually result in problems with the display. The other problem is the wi-fi board goes bad and just sucks all the current when it tries to turn on.
You are welcome to send it to me to look over. However, if it requires specific parts from Logitech, everyone is out of luck. They do no repairs or stock any parts. They will give a discount off a new Touch if the unit is stock. No credit for modded units.