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...
My problem is slightly different but I think related to either the unintentional software update mentioned above or the battery issue mentioned earlier in this thread. We haven't powered off the phone for months and last night I power cycled it. Unlike the
symptom of seeing the exclamation mark or the windows logo temporarily appear my screen is totally blank. It vibrates when I push the power button.
I have tried every key combination and the recovery tool which connected to the phone and successfully did what it needed to do but the device is not detected after the recovery tool. Then it appears in the devices and printers window on my PC just not in
explorer. Tried everything on this thread (paper in the battery compartment, wall charger, PC connection charging and even inductive charging.
My phone is alive as the PC sees it in devices and printers window on my PC! The recovery tool sees it also. At one point during the recovery tool process I think the screen flashed briefly.
This is infuriating.
Has anyone got any other suggestions?
[UPDATE] If your phone is in the warranty period there is a route to get support
https://support.microsoft.com/en-au/contactus/?ws=mscom
Enter the issue once you hit the "get started" button then choose mobile device from the drop down list. You will be taken to an external company support page where you enter your phones IMEI and your details. Then choose a contact option e.g. online chat.
I am trying on a public holiday so will probably have to wait till a work day as am getting no response.
[UPDATE 2] The online chat didn't help. They referred me to log a repair online for the local repair centre. Now logged and will post the phone off on Tuesday