iPhone is not responding at all

Hi Dennis, based on what you say there is a very high probability that the problem is on the logic board. Buying "broken" phones on eBay is usually bad news because these can be phones that no one can fix and then get unloaded on unsuspecting buyers. At least in this case, you kinda knew what you were getting into.

The first thing I would do is to open up your device and do a quick visual inspection. Look to see if the water indicator stickers have turned red. If they have...you may be in for a rough ride :>). Also look to see if there are any missing screws, brackets, torn flexes or any obvious signs of tampering/repair. I once received a phone from someone in Africa for repair only to find out that the previous tech had raided it for parts to the point where it needed to be completely rebuilt before even trying to repair.

If everything looks okay, then measure the voltage of the battery directly with a multimeter. Any voltage less than 2.75 - 3V will not be enough to boot the phone. Report back so we can take the next step. Make sure to comment on this answer otherwise I won't be notified.