Lumia 950 won't turn on

This just happened to me today and it seems Microsoft is to blame...

https://blogs.windows.com/windowsexperience/2017/06/01/note-unintentional-release-builds-today/#sehkQoHC7QuWQLeQ.97

If you are part of the insider program and this happens to you... they pretty much say "Our fault. Oops sorry". Only way to fix it is via an OS reinstall. Some people have said they tried doing that but because the phone can't boot it just tells them "Device not found". Well I just kept clicking on "Try again" until it did. As absolutely everyone knows, the whole reason why booting takes as long as it does is because it is busy loading the stuff it needs to run the OS... I just assumed that if this fix that Microsoft claims will work is going to work then at some point during this boot loop it must reach a point where the app can do it's thing and for me it didn't even take one full loop before the app picked up my device, installed the Os and took me to the setup screen...

2 hours to download the OS and 5 minutes to install it... still busy setting it up... ughghghg...

I don't doubt that Mikaere's solution worked, but there is about to be a wave of people (including me) that are showing the exact same symptoms and they have nothing to do with the battery.

Apparently MS has screwed up and released an internal build of WM10 to people's phones. You can read more about it here. The result is that you get stuck in a boot loop - the phone boots to the Microsoft logo, hangs there, vibrates, restarts, hangs again ad infinitum. The only solution so far is to reset your phone using the Windows Device Recovery Tool. 

I'm dealing with this now - it's basically nuked four hours of productivity for me. Quite how MS is going to give me back that time I don't know. Good luck if you're in the same boat. Sucks to be us.

Hi this has just happened to me, when you say a thin piece of paper, how thin? is it just a cut up piece or folded over at all?

I recently experienced this issue too (vibrates, might show MS logo, then goes blank).   I have been using the charging pillow from my old Lumia 920 so the battery was charged and it wasn't a USB issue.

It turned out that the battery is actually the incorrect size for the battery compartment for the phone and it appears that there are tiny tolerances at play.  The first clue was the piece of plastic paper that was in the batter compartment when I bought the phone - I figured it was to ensure a snug fit.

To fix my issue I added another thin piece of paper to raise the batter upwards slightly at the end with the connections, and then I added another piece to the wall of the compartment at the other end to ensure the battery is pressed firmly against the connections.

My Lumia 950 now works again, the battery is full i.e. it was a always full, this was not a charging issue its an issue with the battery not connecting to the electrical connections correctly.

I have a battery on the way, so I'm hoping that I have the same issue as your wife, just needing a new battery.