What memtest does is, it checks to make sure your ram is properly functioning. Do you know how to burn a dvd? Because on their website they have bootable, burnable iso's. All you do is follow the instructions, bootup onto the disk, and start the test!
If that's to technical, the other option is see if you can boot up onto just one stick of ram, then the other. You accomplish this by simply pulling one of the ram sticks out and booting up the pc, then alternating the ram sticks.
Hope you get it figured out!