Hello BizSAR,
Please note that the processor memory controller supports memory speed up to 1600MHz.
Based on the memory model you provided, the based speed is 1600MHz. There are some memory kits that will run at a default speed automatically and most of the times the speed is 1333MHz.
At this point, I recommend you updating the BIOS in your computer. You can access the following link to download drivers for your unit:
https://downloadcenter.intel.com/SearchResult.aspx?lang=eng&keyword=dx79sr
Also, I recommend you testing another kit of Ram sticks, if possible another brand and model, so that we can discard possible issues with the sticks.