I have messed up my install of 16.04. I have made several mistakes. I had initially (not sure how) installed the system to run on the USB drive that I was using for the install. Also, the system (now 18.04 LTS) will only go through the boot menu if it is connected via LAN. I have taken out the battery and disconnected all power connections trying to clear the MB out, and also reformatted the USB drive with another ISO of 16.04. The system is still getting to the log-in screen and my login info does not work. How do I blank the entire system and start over.
You will need to make install media, install Ubuntu, and select format in the setup
Make sure to install to you desired HDD. During the install, just my advice, only have the desired installation drive in your machine.
See how to make installation media and install Ubuntu here