Go here to download memtest. Go to Download (Pre-built and ISOs)
Get the file that is named Download - Pre-Compiled Bootable ISO (.zip)
It should be under v.2.11
Unzip the file once you download it. You should have a .iso file in the unzipped directory.
Go here and download Burncdcc. Open up the .iso file that you unzipped earlier with Burncdcc. Burn a CD using this program (burn at a slow speed (1X))
Now you should have a bootable CD that has memtest on it. This program tests your RAM and ensures it is in good condition. Once you have the CD, you should take out all sticks of RAM from your computer except one.
Boot from the disc, and run the memory test for at least 7 passes.
After this test passed or failed, try the other stick of RAM (if there is another).
Run this test overnight if you want to.
Read this if you have a notebook.
Watch this video to remove RAM on a desktop.