I just completed the very long replacement guide "iPad 4 GSM Front Panel Replacement". The process went relatively well and before I closed up the unit I powered it on and was able to confirm the LCD and digitizer were working and I also logged in successfully and was able to pick up WiFi networks (just to check that the WiFi antenna was okay).

Then I proceeded to button up the unit, trying to guide the funny home button ribbon cable as best I could to close it. Now after it was closed and sealed the Apple logo showed for booting but then just stuck there. I tried a hard reboot (with the power and home buttons) and it turned off but then immediately back on again (which isn't supposed to happen). I thought I damaged the home button ribbon cable so I opened it back up and put in the previous home button cable with the same result. Now I have an iPad which won't boot. I connected it to my iMac and it was recognized and asked to pair but of course with no interface on the iPad I can't get much further than that.

I also left it overnight and the battery died. Plugging it in I got the same symptom - white Apple logo and nothing more. Hopefully there is an easy solution from you repair gurus out there?