Sorry to anyone pointing the problem at Macbook, but horizontal red lines is a monitor problem that is usually caused by only two things.
-Bad inverter cables/soldering
-Driver for different model/corrupt driver.
There can also be comptibility issues between the monitor and pc, but not very often (usually os related)
If you've got this problem try search for latest drivers. If you can manage to pry apart your monitor (unplugged for a day), Check the invertor cables are fully pushed in. If that fails try re-soldering the base connector bit. I had a 6 y o monitor that looked fine untill i wiggled the wire to find the plastic base on circuit board hanging by a thread. Dab of solder and it was good as new :)