First, unplug and plug back in your HDMI connectors on both ends.
If that doesn't work, read here:
Vertical lines on a TV indicate either a connectivity, software, or hardware problem. This guide will help you to troubleshoot the problem.
streamdiag.com
If you can't resolve the issue using the steps above then it's likely mechanical damage or an electronic problem. Did someone decide to clean the screen with too much spray window cleaner or an overly wet rag recently? If so, then that may be the cause.