Make sure that all of your plugins and your video driver are up to date.
What version of AE? What exact comp settings? Render settings? What effects/ features are actually used? Have you disabled potentially critical stuff to test? You need to be a lot more specific.
I have tried every version of AE, but am currently using the latest version (2015.3?). I'm using a lot of effects. The ease and wizz plugin, particle world, drop shadow, curves, keylight. I'm using motion blur and 3d rotation.
using the event viewer, I have diagnosed Kelylight as the problem, however deleting the file and replacing it, and also clearing all of my preferences does not fix the problem. I noticed during my most recent attempt at rendering, it slowed right down after about 2 hours, and my memory usage was 99%.
I'm very new to this, and clearly not very good at it, so any other questions please ask and I'll do my best to find out the information.
Which OS are you on? Have you tried rendering via Adobe Media Encoder?