iPhone will not turn off.
I just replaced the front glass and everything works fine but the phone will not turn off or reset.
You did not seat the power button flex properly or you damaged it.
Along the lines of Jake's thinking, it could be you left the power flex under the logic board. Open up the iPhone and check your work. The power button flex cable connector is possibly under the logic board. If so, carefully take the iPhone apart and lift the logic board so it can be routed on top of the logic board and connected properly.