If your game was crashing I would say it was due to the server lag/overload issues that they are currently working on. However, if you whole screen is going black for several seconds I would say you have a GPU or less likely a CPU thats overheating. Do you have a way to monitor your temps on this hardware? I think a lot of the GPU manufacturers have software on their sites for monitoring stuff (I know EVGA does anyway) and there are programs like RealTemp GT and CPUZ for CPU monitoring.

Also you can just open up your case and see if there is any dust in your fans/heat sinks. Use your finger or a pencil to keep the fans still (spinning them backwards can kill them) and then use a vacum to suck the dust out. My CPU dropped from 98-102c on full load to about 53-57c on full load after sucking the dust out :-)

GOOD LUCK!