Make sure your RAM is on the same channel. The DIMMs are normally color codded.
The .06 of used RAM is modified RAM. That is normal. Windows uses a little bit for different things.
Available just means what is not in use. Virtual memory is your system using your hard drive as extra RAM.
Known as paging to your hard drive. The Available Virtual memory is how much paged disk space it not in use.
For the other 8GB not showing up may be uncompatible RAM. Make sure you have the same RAM.
Check and see if it is compatible with your system. Make sure the RAM is on the same channel.
Blowout the DIMM slots. Clean the RAM contacts. Your MOB may just be maxed out.
Some MOBs can only support 8GB. You can install bigger sticks, but it will only see some of it.
You can also run Memtest to see if your RAM is fine.
http://www.memtest.org/
Happy computing!