My brother's W10 laptop had a boot error. No boot repair would fix it. So I lucked out. I had a Dell Inspiron of another model but figured close enough to make the 16GB USB full Windows 10 recovery USB stick. I read http://windows.microsoft.com/en-us/windows-10/create-a-recovery-drive and selected the " Back up system files to the recovery drive " option. I can't guess why but it took 4 hours to create the USB recovery drive. Yes it was some nano USB 2.0 drive but I add this so you know to set aside the time.

I did not use step 4 of the link given.

The recovery USB stick did boot but did not repair the drive. A quick check with my brother and he said go ahead with a full "reset your PC" as noted at http://windows.microsoft.com/en-us/windows-10/windows-10-recovery-options