IGNORE Below - I clearly had a senior moment and I'm not that old.
 
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I have 4 sticks of 4GB RAM - and used to have 16 GB of RAM. Now my system recognizes only 8 GB. I took out all of the sticks and tried putting in one at a time and each one was recognized as 2GB in the startup screen.
 
What the heck happened? I'm basically seeing half the RAM and since each stick is registering the same amount I imagine this has to be the motherboard? What should I do?

Even CPU-Z is reporting it as 2GB sticks in each slot and they are 4GB sticks.
 

Ok, I clearly was a dunce, I swore I had 16 GB of RAM - I must have read those labels on the modules wrong since they were pairs of sticks so that must have meant 4GB total for both and not per stick.
 
I've had this motherboard and RAM for 7 years - YES, 7 years, and this is the first time in like 5 years I've looked inside it because my system was going super slow in a game.
 
Thank you for making me whip out the manual to verify - you are correct: 8GB max.