We turned off the breaker to a room, replaced all the wall sockets and turned the breaker back on. Now there is no electricity. Any idea why?

Does it trip out as doon as you turn it back on? Could be that you have a dead short , which means when you pushed outlets back in you have a ground wire touching a hot wire. Pull them out , make sure wires weren't touching . Before you push outlets back try turning breaker back on to see of it holds. If that's not it pull outlets back out and make sure you wired them correctly! White wire to the silver screw black wire to the copper screw and ground to the green screw .

Hotwire is on the right road. Does the breaker actually fully flip and stay flipped or does it trip? If you can't tell us which then we are stuck.