Doug, you said the screen had vertical lines on it, but you didn't say if the screen was readable or not.

If it's a readable screen, you can do as I said before, hold Command+R while booting the mac to go into "recovery" mode where you can erase the disk from that screen.

If the screen is not readable, you can boot the Mac into "Target Disk" mode by holding "T" while booting, and then if you happen to have the right kind of cable and interface (possibly on a PC or on another Mac), such as a FireWire cable or a Thunderbolt cable, you can connect to that Mac as if it were just an external disk drive, and wipe the disk that way.

https://support.apple.com/en-us/HT201255