Please type Resource Monitor into Start Search box, rightclick result to run as Admin, click on Memory tab and post back a screenshot of the chart showing RAM apportionment.
Test your RAM - Test with Memtest86+.
There are specific steps to test both RAM and slots.
Swap your RAM sticks, check for debris in slots. Run Sticks individually to check detection, then add another stick to check again.
Remember to touch metal on or inside the case before touching any chips or components, to avoid ruinous static discharge.