If you took the display off then put it back together, try resetting the phone by holding the home button and sleep/wake button for like 15 seconds, or as long as it takes for the apple logo to come up. Sometimes that works. If not, you might have damaged the LCD. try replacing it. There are tutorials on this website on how to do so. It's just a couple of screws to separate it from the digitizer. If a new LCD doesn't work, then it very well may be a broken coil or circuit on the motherboard. But try the reset or replacing the LCD. All you need is your new part, a 00 phillips head screwdriver, a suction cup, and a plastic spudger. Good luck and let us know how it turns out. EDIT: I'd also try looking at the pins on the connection between the LCD and motherboard, Sometimes they bend or snap and that could explain why you're not getting the same "click" when plugging it in.
If the phone is AT&T, when you open the phone and look into it from the back, there is a screw in the top left just below the rear facing camera which acts as a ground. Replace that screw with one of a similar size that will fit. That solution has worked for me. However if that doesn't work you might just have to replace your dock which holds the microphone.
If you changed the sensor cable then you changed the sensor. They are attached and cannot be removed from one another. Make sure your orientation isnt locked. Also you can put a piece of electrical tape between the prox. sensor and the ambient sensor to make sure they arent interfering with eachother. Update: You can lock or unlock portrait view on the phone. To do this, double click the home button, swipe left in the app switcher and you'll see the lock/unlock icon on the far left.