windows 10 password failure

I recently upgraded to windows 10 from 8.1 and was pleased with the smooth change over. But, my pc has locked and no password works!
Administrator password doesn't work. Even in safe mode it asks for a password and that doesn't work either! I've tried several "fixes" on this site but so far nothing works. By the way, I don't have a password reset disk nor the cd for windows 10 since this was an Internet upgrade. Can anybody help?

Thanks Bunnyj! I set up under gmail. Will that matter?

Thanks for the help. I'll let you know the results.