A service manual for this is going to be impossible to find to figure out what's going on, unfortunately it's most likely not fixable, one thing I can tell you however is powering it up with a cable unhooked won't hurt anything
Vertical scan failure. Contact any service technician. If you wish to get some details; check the sites linked here.
Faults & possible causes to LCD screen are given with illustrations. You can get an idea about the fault. Search the site by type in the Brand Name of your set, in its search bar at the right side column, and press enter. See it in by Webview with mobile or by desktop. Mobile View has no search box. Screen-shots to defective LCD panels are given. You can see and compare to that to your TVs', and can make sure about the fault to an extent.