Take a visual (look) at the VGA connector from the monitor for bent pins, then refasten it to the computer. If still bad, try the monitor on another machine. Just FYI, repair costs usually exceed replacement costs.
Tip: See if the place you get the monitor from will dispose of your old monitor for you.
after problems with my pc, my monitor isnt the same colour as it used to be and is sore on the eyes to look at, its giving off a green/blue colour.