Try each stick by itself. If they all boot by themselves, install 1 bank. If that works, take those 2 sticks out and then try the other 2 sticks. If they work, enter the BIOS and raise your memory voltage slightly, we are talking about tenths of a volt, and try, you can go like 1.9, 2.0, 2.1. 2.2 is about the highest I would go. It is normal, especially with DDR2 to need to raise the voltage slightly to get it to run stable when you install 4 sticks.