Please provide more detailed information on your system in order to help you. For example...
What is the BIOS version installed in that computer?
What is the part number and manufacturer of the memory sticks you have tested with?
What is the model and wattage of the power supply installed?
Please let me have the AA number and Serial number of the motherboard. The following link provides information on where this information should be located on the motherboard: (The serial number is on the left of the AA number)