My alto sax suddenly started to squeak, and I can't play low D or high F-F# anymore.?

I'm not sure if that dollar trick would do anything... if you did it too hard, maybe a pad got loose. You could very well have a leak. Check your pads, see if the grooves on them are lining up on the holes. You could always take of the pad and readjust it yourself, and glue it back on with hot glue, but I suggest you just take it to your local store.