How to fix a sunk in power button

So, my iPhone4 was perfectly fine until a couple weeks ago. I took it out of my pocket and I discovered that the power button had "sunk" in. It still functions; however, there is no click or resistance when I press it down. I have to push a lot harder in order for it to properly work. I have take then entire phone apart in order to attempt a fix, but I cant figure it out. The power sensor cable seemed perfectly fine (the yellow 'nub' was still intact). Any suggestions on what I can do to restore the original function and regain the clicking?

Any help would be greatly appreciated.

also, theres no water damage nor has the phone been dropped.