Iphone 6 plus IOS 8 will only display the apple logo when turned on or connected to computer
This likely will not help everyone experiencing this type of issue, but this is how I got it working again.
Once I saw the connect to itunes screen, I did that.
Next it started on its update
After the main download and install it displayed a load bar under the apple logo again
Now its working, its updated
hope this helps someone