Have you tried re-seating the stick(s)? Typically, there's a small panel on the back with 2-4 screws, remove them and you'll find the DIMM of DRAM held in place by two small clasps, they generally ease to the side and you can remove the DIMM, blow in the socket and replace the DIMM the same way it came out as there's a small notch in the DIMM that fits over a protrusion in the socket and give it a try