I built this computer over a year ago with an ASUS P5N-D mobo and 2 x 2 GB of DDR2 PC6400 ram. It has always worked great. Then I decided to upgrade by adding 2 x 2 GB DDR2 PC5300 so it had 8 gigs total. When I turned it on it would not post and made 1 long beep then 2 short beeps - which i believe means it can't read the ram. I took out the new ram and went back to the original configuration and it still has the same problem. Did I do something wrong, what should i try next?