I have changed the OS of my computer to win7 64 from vista 64. It works fine with 2 gb of memory. When I tried to install another 2 gb on the ASrock mobo (939S56-M) it would not boot up. I have increased the range from 2gb to 4gb. Crucial and Asrock both state that it can take 4 gb. All the memory modules are new form Crucial. The Bios is P1.30. Please could you suggest how I can fix it?