Put everything on default in bios inlcuding RAM speed, just to exclude the problem from speeds. Take out all memory sticks and put only your original sticks (16GB). Let's see if PC will be working fine. If it's working and doesn't do blue screens, then now slowly start adding your new memory sticks.

A lightweight system today can get by with 4GB of RAM. 8GB should be plenty for current and near-term future applications, 16GB gives you comfortable space for the future, and anything over 16GB

It can be listed as memory remapping, memory extension, or something like those. Adjust AGP video aperture size in the BIOS and test. Its possible the memory it was using was locked by the video card. You could try just the new RAM to make sure it works with the CPU. Try the lower voltage RAM in bank 0 moving the older RAM to bank 1.
When you have an empty memory slot, or you install memory in mismatched capacities (1 x 8 GB + 1 x 16 GB for example), the memory runs in the lower performing single data rate (SDR) mode. When you install memory in matched capacities (2 x 8 GB or 2 x 16 GB), the memory runs in the better performing dual data rate (DDR) mode. Watch this video
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can i add 16gb ram to 16gb ram