Computer Freezing

I was playing with the Torque3D 2009 trail in "play" mode and then my iMac suddenly flashed to black for a tiny second twice and then it froze for like a minute, after that i was able to use my machine but it stuck and froze all 20 seconds.

Any idea?

iMac 20" Early 2009 2.66Ghz
NVIDIA GEFORCE 9400M
4GB RAM
10.6.3