I'm at a bit of a loss here. I have a Verizon M8 Windows Phone that had a dodgy touch screen, but the LCD was fine. I...

I believe there is a problem if the phone is playing music with BoomSound on and then a call comes in, it can screw with the earpiece settings. Try turning off BoomSound and then reboot the phone.

I can vouch for this heating method. I purchased a 4S with greyed out wifi, and n/a for the wifi address under the settings. The bluetooth was showing an address under settings but would continuously be initialising itself. I removed the back, battery and EMP shield as per the instructions above, and warmed the wifi chip with the tip of my soldering iron for a couple of minutes (I don't have a hair dryer). I re-assembled the phone, turned it on and BAM....the bluetooth was on straight away. I went into wifi, which was now no longer greyed out, selected my router and connected. I can turn the wifi and bluetooth on and off and they connect successfully every time. 100% perfect result!

I have exactly the same issue. Iphone 4 wont turn on unless connected to PC, and continually goes through a boot loop. I'm guessing a bad battery. However, I went one step further. I have one of those battery pack cases, so I put my phone in that. It turns on fine and boots up ok, but itunes will not see it. Shortly after I plug in the USB cable, it reboots and goes back into the boot loop. If, however, I put it into recovery or DFU modes, then itunes sees it ok. Restoring brings up an error 1394 every time. I'll replace the battery and see what happens.