The first building at the bottom of your screen has a gang in it. You have to fight them. Have enough stimpacks to last you and some good armor. After you have killed the gang got to the back room in that building and release the guy in there. He asks you to tell Talus He is ok.
Talus is at the brotherhood of steel.
He will give you a list of weapons and power armor. Tell him you want the power armor. Then you have to go and see Micheal. Micheal gives you the power armor. Click it and she will join you.