DIAGNOSIS Signal integrity issue or a failing connection between the panel and the T-CON board. Often appears as vertical lines on one edge.
FIX Reseat all internal connections. This requires disassembly. Unplug monitor. Remove stand. Carefully open the rear plastic case. Locate the thin, flat ribbon cables (LVDS or eDP) connecting the mainboard to the panel. Unlock their connectors, remove the cables, clean contacts with electrical contact cleaner, and reseat firmly. Reassemble.
IF THAT DIDN'T WORK The panel itself or the bonded driver chips on the panel's flex cable are defective. This is not user-repairable. The symptom indicates a physical hardware fault requiring panel replacement.
HEADS UP Static discharge can kill the panel drivers. Wear an anti-static wrist strap when handling internal cables and boards. If you're not comfortable, do not attempt—seek professional repair.