Welcome to Justanswer.com, my name is ***** ***** I will do my best to assist you.
To get started, I need to know what type of computer you are using, a Windows XP, Vista, Windows 7, Windows 8, Windows 10 or a Mac.If its a Mac, please check the OSX version as follows, Click the apple sign at the top left of your screen, then click about this mac. And then where it says version, send that to me as a reply.
You could try factory restoring the computer.. For which you wont need an administrator account or password.. Be warned though, this will erase all your documents, files, etc and reinstall windows and the gateway software and drivers.
Your only other option, would be to create a password ***** cd, such as Hirens Boot cd and then follow this guide to use it to change the password.
Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.