iPhone 5s: No screen or vibration after battery replacement

I used the iFixit kit to replace the battery in my iPhone 5s, but now the screen is black and vibration seems to be broken. The phone is detected by iTunes when turned on, and I was able to put it into DFU mode to verify that the home button works, but that's all it can do now. I even tried disconnecting the new battery and connecting the old one, but nothing changed. I didn't remove the screen for the repair, because it seemed like more trouble than it was worth, but I did open it up a second time and tried de- and reattaching the LCD cable, with no effect.