Many ways to look at this. Some failures are time dependent rather than use dependent. Some time has passed. Some failure are vibration or shock dependent. It has been moved so that could cause those. Some failures are caused by accidental mishandling which could have been caused by a cleaning lady or something unexpected during storage.
It could not be a failure but just a mispositioning. My DAC has pairs of RCA connections vertically and for some reason I tend to hook them up in horizontal pairs and then I have to figure out why one channel isn’t working.
Hopefully your failure will be fairly easy to diagnose.
I assume you mean the tubes aren’t lighting up. If multiple tubes aren’t lighting up that points to a fuse or powr problem. I’d open it up and see if there is an internal fuse.
If tubes are lighting up but no music, make sure you have all the connectiions correct. Make sure you don’t have a switch in the wrong position. then replace any tube that feeds both channels.
Jerry