Why wont my galaxy S5 boot after changing mid-frame?

My galaxy s5 had a broken screen and a dented frame, so i decides to replace both. i checked the screen before doing anything with the mid-frame and it was working perfectly. So i removed the screen carefully and unscrewed the mid-frame and replaced with new mid-frame. when i plug my screen back in and try to power on the phone i got nothing. The phone does not even vibrate when holding the power button. I also tried holding volume down, power,home button all together to see if the phone would boot and still nothing. lastly i took out the battery unplugged the phone and held the power button for one min and then put the battery back in and still nothing . Is there something i am doing wrong? Please help!