My 8 cores PC feels like 2 cores processor

I bought a Novatech Barebone. It comes with ASUS M5A97 LE R2.0 Motherboard and AMD FX-8320 8-core processor, 942 CPU and 8GB DDR 3 RAM. When I purchased it, everything comes pre-installed and they told me this is the best specifications in pre-over clock. However, it doesn't work like an 8-core CPU. Just today, I tried to render a 5-mins. Fraps recording from the MMO game. During the process, my CPU usage became 99% in an instant. The 8-cores max up and the temperature on my CPU became 79 degree Celcius.
I wonder what could be the problem here?
