Try removing the memory and cleaning the "gold teeth" lightly with a clean eraser and then wiping them clean with a very small amount of isopropyl alcohol or electrical contact cleaner and making sure the slots in the motherboard are blown out and clear of dust or particles. Then reinstall the RAM.
Go into the BIOS and reset the BIOS to the default or optimal settings. In fact, you can try this first if you prefer.
Run Memtest86 on each memory module separately, not together, for seven passes to test them for errors. Basically you want only one module installed while you test them and make sure that the one module which is installed is in the correct slot for single module operation.
If none of that turns anything up, test the hard...