I have a Microsoft Lumia 435 and tried to install the Windows 10 preview. It was updating and showed the two gears moving. It was almost complete when it turned off, rebooted, and showed the gears again. Then it turned off and repeated the process. It keeps doing this over and over again. How do I fix this problem? Any answer is appreciated.
I had a similar problem with my Lumia 625 as shown in this thread here.
Although I am not entirely sure what the issue was, it appears that I (and others) was able to successfully update to W10 Mobile Insider Preview following the reboot loop by choosing Slow Updates rather than Fast Updates.
If you are unable to get the update to complete you may have to do what I did, which is as follows ...
- If possible, do a complete backup of all data on the device.
- Do a complete reset using the Lumia Software Recovery Tool which will wipe all data from your device.
- Using the backup, restore the data on your device (if you were able to backup the data of course).
- Retry installing W10 Mobile Insider Preview using Slow Updates rather than Fast Updates.
Further info on recovering/reseting your phone software can be found here.
Given that Windows 10 Mobile is still in the preview stage, I'm going to guess that a build got released that didn't quite agree with your specific phone.
I think at this point your best bet would be to temporarily revert back to Windows Phone 8.1 using the Windows Phone Recovery Tool and then decide whether you want to reinstall the same build or wait for another one to come out.