Can we please see a screenshot of your memory and multiprocessing settings?
Also, what makes you think it's not using more cores? Your screenshot isn't particularly helpful because I don't know what it's from or what it's showing.
Try running the Resource monitor and watching the performance on all of the cores when you start a render.
Previous screenshot was from Task manager > Processes , ok I'll check resource monitor, I didn't know about that.
Search this forum. There is an endless number of threads as to why and when AE is only using one or 2 cores, how to set up MP rendering, improve performance and all that. No need to add yet another such post every week.
I asked because obviously I couldn't find it in search, either search engine is not that good, or those threads are using different keywords.
See this to understand how CPUs are used by After Effects:
You won't always see all of your CPUs used at 100%. There are a lot of other components to rendering, and the CPU is often not the bottleneck.
See this page for resources about making After Effects work faster: http://adobe.ly/eV2zE7
See this page for information about hardware for After Effects: http://adobe.ly/pRYOuk