this is a common issue with ati/amd video cards as they get older. Once it starts it will likely get consecutively worse over the course of a few months until it is an every time kind of issue. A temporary fix is to completely uninstall your gfx drivers and reinstall them. This will make the freezing less frequent and hopefully stop it entirely for a week or two. The only permanent solution is to replace your gfx card. I highly recommend going with a nvidia card as they tend to have less problems.
I don't know where you live but if you're near a microcenter I'd suggest perusing the clearance rack they have there as you can usually pick up a 560ti for around $80 or a 660ti for about $130 or even a lower end card (it doesn't sound like you need a 560 since you only play css and dods) for less than $40
*Source: I build, repair and upgrade computers for some extra income on the side and this is something I run into on at least a monthly basis.