The poor quality of the question doesn't give us much to work on but the picture could give us a better clue (and from previous experience of seeing similar screens)
- It could be a CPU/heatsink heat problem (the machine looks quite old so the thermal paste may be cracked/failed)?
- Your graphics card may be broken/overheating? If it's "on-board" GPU then a new motherboard would be required. An external GPU then try removing it and connect your screen to the on-board graphics card.