Today I bought a new Behringer TU-300. When I plugged the power supply in, the cables and tried to turn it on, nothing happened. Tried it with different cables and with a battery, nothing. It doesn't turn on at all. Does anyone know what could be the problem?
Doesn't matter. Send it back for warranty repair. You've done a thorough job in checking the basic issues, anything more complicated than that is not worth trying to fix if it's under warranty.