test your installed RAM with Memtest86+
http://www.memtest.org/
Click on Download (Pre-built & ISOs).
Click on Download - Pre-Compiled Bootable ISO (.zip)
When downloaded, unzip the ISO file from the zip folder.
Now install IMGBurn from here: http://www.filehippo.com/download_imgburn/
use IMGBurn to create a CD from the memtest ISO file.
boot your PC from that CD and Memtest will start automatically when the CD has loaded.
Let Memtest run for at least 3 passes before stopping it (<Esc>)
If errors have been reported, shut down PC and test each RAM module on it's own to determine which one is faulty.
Or you can test each RAM module on it's own from the outset - up to you.