while upgrading my windows phone to 10 it stopped in middle because of power problem.now i am unable to start my windows phone and even i tried to hard reset but it doesn't work.when i connect my phone to power adopter it just keeps restarting. moving gears comes and then phone restarts again and again .please help
Have you tried downgrading your phone to back to Windows 8.1? There is already a detailed explanation of how to do this in the question, How to rollback from Windows 10 Technical Preview?
It is a simple process, but you will lose almost all of your data saved onto your phone. Follow the directions given here by Microsoft. You basically just download the Windows Device Recovery Tool, connect your phone to your computer, and let it run.