Welcome to Android Central! Which phone? That's a form of factory reset protection, to discourage thieves from stealing a phone and doing a factory reset to make it their own. You could try a hardware key factory reset, but you'll still have to enter the Google account and password associated with that phone -- hopefully you remember that. To learn how to do a hardware key factory reset, either tell us which phone you have or do a search for "[your phone model] factory reset."