Replaced physical power button. Unit still not turning on. Switch?

After a bike accident, my iPhone 3GS refuses to turn on and off when pushing the top power button. I can use the phone normally by pressing the home button and waiting for the unit to go blank after using it.

I assumed the power button wasn't working so I replaced it today. If feels better when pressed but the unit still refuses to turn on and off. Is the switch (microswitch?) underneath the power button defective? What do I need to replace?

I also want to add that the back case has some cracks but it is underneath a decorative sticker. I don't see any signs of relation to the power button though.