When the A key doesn´t close propperly,the instrument will be unplayable. Check with a piece of cigaret paper, which you place under the A pad, if you have a firm grip. If not, take of the G# key and then the A key, and make sure that there is no corrosion on the A spring as well as the little sping which is mounted inside the A spring groove. Sometimes this spring might also be pushed out of it´s place. In this case push it back. In some cases the A spring might also be pushed toward one side of the groove, which disables the A key to close either.