iPhone won't turn on at all!

I purchased an iPhone with no water damage no icloud lock and clean esn

the iphone had a broken screen which I did not replace yet

but it would turn on and get to the home screen without problems except the display

since I was waiting for the new screen to arrive I left it on my table without any one touching it

When I came back home I tried to turn on the phone but wouldn't respond not even the battery low logo when there is no battery and the cable is connected

I tried holding power button and home button for 2 minutes with no response

left it to charge for 24 hours still no response

connected to pc while trying to hold the home button no response

also in dfu mode no response

iTunes does not recognize anything connected to the pc at all

don't know what to do going crazy!

I also tried dissasembling the phone and put the motherboard aside for about half an hour maybe it needed to reset but still no response

Please help!

Thank you