2012 Mac Pro Loses Icons and Text

I am using a 2012 Mac Pro 12 core tower with 24GB RAM and a 500GB SSD running OS 10.9.5. Along with the Radeon 5770, I have an Nvidia Quadro 4000 installed.

After a few hours of heavy graphics work in After Effects CC or Cinema 4D I find that this sometimes happens. I lose icons and some text, and the computer slows down to the point that it unusable. A reboot fixes it, but I would like to know how to permanently fix this issue.

Thanks!