Hi I have a Dell inspiron N7110 17 inch laptop and i'm selling it so in order to remove all the data i'm trying to perform a reset from the update and security options. (ps. I have update the software to windows 10)

Frist i tried this around 7 times and it got stuck at 1% .. and now after the 8 th time, it has come to 66% but then it says that the reset couldn't be carried out and theres only the option to cancel. Then i tried it again it goes up really fast to 66%, stops and tells me the same thing. Can anyone help please?