RAM Problem SOLVED

I'm not sure if this is the right place to post my problem but here goes. A month ago I upgraded my RAM from 6 To 12 GB. I had  no problems installing and it showed at System Info that I had 12 GB of RAM installed. Two weeks later I added a Hard Drive for storing project files etc. No problems there. This morning my PC seemed to be running erratically so I called Microsoft Online Support. They checked out the system and did this and that but when the tech went to System Info it showed 11 GB of RAM. I told him about installing the 12 GB RAM so he checked files etc.and  said I needed to speak to the people that I bought the RAM from. He thought one of the sticks may be bad. I contacted Memory Stock support and they had me reinstalled all the sticks. After doing all that it still showed 11GB of RAM. Memory Stock support said that I have a software or hardware issue and I need to take it to a PC repair store. They said if it was a bad stick it would show 10 GB of RAM. So any help or guidance is greatly appreciated. My PC seems to be running fine but it still shows 11 GB RAM. Thanks