Have you tried one stick only of memory? (Not sure if that is what you meant by swapping memory one stick at a time.) If not might be a good idea to check.
Is the memory on the mobo list of compatible memory?
Did you connect the power cable to the video card?
After going through the no boot checklist linked above, if you still have problems:
1. Please provide a complete list of components with full model numbers.
2. What happens exactly when you turn it on? What lights, sounds, fans, etc. if any.
3. Can you try the graphics card in another PC to verify it is good? Also the cable.