Shure Beta 58A Professional Microphone "voice turns right back again" Questions

...voice harmonizer.That improved the sound of his mic, its a lot brighter now, but I am the only one with feedback problems. Why? We use mackie smr 450 as monitors and they are put in front of us. ...

...voice AT ALL goes through i tried all different things: -made sure it wasnt muted -turned it up -tried every plug in the back of the tower -tried every audio input and it still wont work please help! ...