|There are several causes for this, the first one is quite easy to fix|
1. Update your graphics drivers
Newer graphics drivers fix bugs and add features that may fix your problem. You can find newer graphics drivers on your PC manufacturers website, or from Intel, AMD and Nvidea.
2. Clean your computer out
If your computer is overheating, applications and games will act slowly or strangely, if not crashing. If you have a laptop, the best method without opening up the case would be to blow some compressed air into the air vents to blast the dust out.
To clean a desktop, you will need to disconnect everything (especially the power) and clean the case. You should know what you are doing when opening up a computer, as there are lots of delicate and dangerous components inside.
If you feel confident that you can open a computer, clean it without damaging yourself and put it back together, here is a link to a tutorial. This is a very extensive tutorial, and you could probably improve things just by using compressed air to remove dust from inside.
If you do not feel like doing it yourself, most computer repair shops offer a cleaning service.
Hope this helps, and post back with your results