You should bring it to a service center, sorry. For further help take a look at the line6 homepage under "Support" -> "Customer Service" like this:

http://line6.com/support/docs/DOC-1606 . This will result in a relieable device / piece of work.

It may have a sticky switch problem, but also may have a contact problem to the circuit board, or somehow gets a short circuit.

Only if guarantee is over and you have experience with electronics / soldering etc, you may try to open the case and have a look inside and resolder / do some isolation. But even if you discover the problem - you might need and do not have replacement parts.