do you have a multi meter? check for voltage, if it has 12v at the power side check the ground, if theres any voltage reading on the ground you have a bad ground, if you have no voltage on the power side then you have a blown fuse or bad relay. id put money on a bad fuse or relay or burned up wire. if you end up with a burned up wire its probably due to excessive resistance from a worn out/bad blower motor, i doubt this is your problem since you lost all of your speeds at once.