Hello and welcome to windows central. Did you have w10 mobile on your devices? What happened before you had this? You may make an account in order to reply to this thread
This sounds like just my problem I had with my 520. It did have also:-( (also after reset) I fixed it but I need to know some things have You tried WDRT? Does your device have removable battery?
If WDRT doesn't detect your phone restart it and when on spinning gears pull the battery out. Don't leave it connected to your pc .Somehow this made my phone detectable for wdrt and i could reflash the ROM. Repeat the process if it doesn't work the first time.