Hello, Have you tried to replace the battery? If the battery fails or the circuit attached to the battery it will send the phone into a boot-loop. If the phone can't communicate with the battery via BSI to verify the battery temp amount other things it will send it in a boot loop. This is why when you connect a DC power supply directly to a iphone and not power it via the battery the phone will go into a boot loop. I forget what apples calls that on their schematic... Point is try to switch the battery... If not come send another message...

Try holding the power button and the home button for like 10 seconds... Sometimes I find they need to be reset to reconize the new lcd...