HELPPPP! I was just playing around and pressing some keys, I don't know which ones, on my alto, and now I can't get it back... It must have happened to others here, mustn't it?
Another problem I'm having is finding the sweet spot of placing the mouthpiece, after I remove it from my mouth and start again. Sometimes I get it and with a good long breath, hit nice clean tones, and the next time, there'll be strangled squeaks and burps, which is only to be expected for an absolute beginner. When I was able to put a run of 6-7 random notes together, on either the left or right keys alone, I was pleasantly surprised by the depth of the notes I was able to reach. In order to get it down, it's going to be just a matter of trial & error and then muscle memory.
Some of the aforementioned squeals, possibly unintentional altissimo, hold the promise of higher notes when I get things under control.