I have this happen with my computer at times too especially when I'm working on huge projects. I was told by a Computer guy that it's a good possibility that it's my Video card and that I should updater the Driver.
I would find out what Video card you have and update the driver~ See if that helps. It's free to update your video card driver~ Cheaper than replacing your monitor just yet. The reason I know mine is not from my monitor is that I've hooked the monitor up to my other computer and never had that problem. Since I've updated my driver I haven't had those problems.
((hugs)) Mechelle