I had an IT and it doesn't have a mute or standby, from memory. Is it new for you, was it working OK before? You could look under the lid, but it may not be helpful with Solid State kit. I couldn't tell if a capacitor was blown, without a circuit tester, even if I knew how to use one.
It may be worth checking the input source, try a different one if you have one. Otherwise I would take it to a tech to check it out.
It may be worth checking the input source, try a different one if you have one. Otherwise I would take it to a tech to check it out.