http://www.pcadvisor.co.uk/how-to/pc-upgrades/how-check-for-bad-ram-modules-in-your-pc-3432631/

Testing with Memtest86

In comparison to the Windows Memory Diagnostics Tool, Memtest86 is often regarded as the more thorough solution. As a drawback, it also requires slightly more preparation to utilize: Memtest86 comes in the form of an ISO-Image, so that you will have to burn it on a disk with another program (such as ImgBurn or Hiro Burner) before being able to use it. In addition, you might need to have a look into your BIOS settings first to ensure that your boot order prioritizes your disk drive in favour of your hard drive, thus making sure Memtest86 won't simply get skipped while booting.

If everything is in order and ready to go, restart you PC with the bootable disk to launch Memtest86. Once inside the main menu, press 1 and Enter to load the latest runtime version. The testing procedure itself will begin automatically after a couple of seconds and go through eleven dedicated routines, testing your RAM's ability to save data discretely as well as safely. Unsurprisingly, this might take some minutes to complete and can be fairly confusing to watch, so don't worry about that.