Monitor has a tint of one color
Monitor cable is defective
Temporarily disconnect the monitor from the back of the computer and verify that there are no bent, burnt or broken pins. In the picture is an example of what a VGA connector cable looks like and the VGA connection on a computer. Your computer may have this cable or a DVI or HDMI cable.
If the end of the cable appears to be fine, reattach the cable and ensure it is firmly connected to the back of the computer. If you continue to experience the same issue, continue reading through the other possibilities.
Monitor is bad
If you have verified that the cable is not defective and is firmly connected to the back of the computer, it is likely that the cable connected to the monitor or the actual monitor is bad. It is recommended that it be serviced or called in for repair through the monitor manufacturer.
On some older CRT monitors you can give it a good slap on the side of the monitor which can fix this issue, although usually it is only temporary.