Stuck at spinning wheel on boot.

When I turn on my iPhone 4 it will show the apple logo for a few minutes and then a black screen with the spinning wheel appears. This wil keep on spinning for ever.

The home button has been replaced by someone else a while ago.

iTunes detects the iPhone and I can view its properties. Syncing doesn't work.

I tried to restore it in DFU and pwnd DFU mode but in the end it always ends up at the spinning activity indicator on the black screen.

Does anybody know something else I can try? Or maybe know what the problem coal that causes this?

Thanks in advance.

Edit:

I took the whole phone apart. Couldn't find anything that could be the problem so assembled it again.

Afterwards I disconnected the cable with the Sleep/wake button and Proximity sensor: iPhone boots as normal and everything works like a charm!

Seems like one of the components on that cable is not working correctly, causing the phone to hang on startup.

I will replace the defective cable with a new one, lets see if everything works again then.