My motherboard has 2 X DDR2 slots and 2 X DDR3 slots. I recently bought 2 X 4GB DDR3 sticks to put into my computer. I am currently running 2 X 2GB DDR2 sticks. Are the two RAM types compatible? When I installed the DDR3 RAM my computer will not turn on. I have yet to try to take out my DDR2 sticks and just use the new DDR3. Will that make a difference? Thanks.