Microsoft account-based email address locked out of PC

My father in law has Windows 8 he accidentally put a non working email address in on the windows 8 log in . He did not set up a disc to reset his password either . How can I reset this non working email and get him logged in. He is 72 years old so he just made a mistake. His PC is an HP and he bought it from Walmart it did not come with any software. Thank you very much