Microphone Not Working With Focusrite Scarlett Solo 3rd Gen

Hello,

I recently bought a 3rd gen Focusrite Scarlett solo audio interface and have been recording in Garage band. I am able to plugin my guitar through the inst input and record, everything seems to be working fine. However when i try to plug a microphone to the XLR input on the audio interface to record vocals or an acoustic instrument it doesn't seem to work. i am using a Shure SM58 microphone which works otherwise but when plugged in to the Focusrite the light doesn't turn green and it won't let me record anything. Does anyone know why this may be and if so what i could do to fix it? Thanks.