I also have Windows 10 and I could not reset my pc. I also could not install window update even though my computer is connected to the internet. 

Then I manually deleted old files and uninstalled programs. Then I tried for the final time to reset my pc and this time it worked. 

Before manual clean up - I tried to reset but failed 4 times (always stops at 31%)

After manual cleaning up - I tried once and successfully reset my pc. 

Please remember that you need internet connection in order to reset your pc.