You are going to have to test RAM multiple ways.
oliverpowell is correct about the slots.
RAM stick in Slot 1 call it RAM Stick A
RAM stick in Slot 2 call it RAM Stick B
Test:
- All RAM in PC
- Remove RAM stick from slot 2 (Stick B). Test the RAM stick in Slot 1 (Stick A)
- Remove RAM from Slot 1 (Stick A) and place Stick B in slot 1.
- Place Stick A in slot 2, now all RAM is in the PC and test.
This will take a while but it is the only way to find a fault in the RAM or in the motherboard RAM slots.
EDIT: Yes you will need to run each test for at least 10 passes. Sorry.
EDIT: Probably print this and that way you can mark off each test as you complete them.