If you didn't see the Samsung logo when turn on the phone or any back light on your S4 since you dropped it, you must need to check the LCD screen connector and check the pins on both the cable connector and on-board connector. If they are okay, replug the connector and to see if can work. If not, replace LCD screen, see more info [http://www.witrigs.com/replacement-parts-complete-lcd-screen-with-digitizer-and-frame-for-samsung-galaxy-s4-gt-i9505-black-mist-oem|here].
As for power button, it's easy to replace. See [http://www.witrigs.com/replacement-parts-power-button-for-samsung-galaxy-s4-gt-i9505-oem|here].