If the machine isn't new, just first take out the Memory Modules and use an Pencil Rubber for to clean the Connector Feet's. If you have ore than 1 module and the problem still exist, start to replace them one by one which restarting the machine by every one to find out which is trigger the problem. Also take some Air-Blaster to "clean" the sockets. It's possible that the whole is resulting from air moisture etc.!