If the rear is working then the MC is not the problem. What exactly did you do when changing them. Did they work BEFORE you FIXED them? Did you open the bleeders and let air in the system? Is the reservoir full? Have you pumped them a bunch of times to see if they will pump up? It's pretty unlikely that BOTH front calipers would fail at the same time unless you did something to make them not work. Did you compress them just enough to get the pads on or did you squeeze them down very hard? Did you have the top off the reservoir when compressing so the fluid had somewhere to go?
Need more info to try and help you.