RAM ?

try re-installing the ram in diffirent slots and if not, go into your BIOS setup and check how much ram it says are available there. If its less than 8gb then there is a hardware problem. Otherwise, double check you installed the 64 bit version, thats the kind of message you normally see with a 32 bit system. If you right clock on My Computer and go to properties it should tell you if its 64 or 32 bit.