does not turn on but recognized by itunes

My 5c does not appear to turn on. The screen is dark and when the power button is pressed and when both power and home button are prressed nothing happens. I have tried all the reset solutions available. I have also opened up the phone to make sure all cables were connected.

Even though the phone appears to be off, when it is connected to iTunes, after a few minutes I see the folowing pop-up message:

"itunes could not connect to the iPhone "phone name" because it is locked with a passcode. You must enter your passcode on the iphone before it can be used with iTunes". The phone also shows up in explorer as a storage device. These two items occurred before I disassembled the phone so it is not that something was done wrong putting it back to gether.

Do these symptoms mean that the battery is good and the problem is the screen? Before I order replacement parts I want to make sure I get the correct part. Is there any way to make sure what the root problem is?

Thanks, George