Before you take it to repair try:

1. Unplug HDMI cables (just one end on each.) Remove power from both display and TV. Wait 10 minutes then apply power and only the cable needed. Retest. I won't write about basic product use, selecting input, setting PC resolution and outputs.

2. Try other HDMI sources.

3. If the above fails, get estimates. Repair rates for OOW products often are more than a new device.

4. As to what it could be, usually fried chips on boards. Why is usually some surge or other bad thing happened.