I purchased a w520 with 4gb of ram (2x 2gb) about two months ago and recently received some additional SODIMMs to populate the other two slots. however when ever I use either of the two remaining slots (the one closet the system board under the keyboard, and the free slot on the underside) I get the beep code 1-3-3-1.
I've tried mixing and matching the combination of dimms (new only, old only, and one of both) and they work fine as long as I only use the original two slots and not the two free ones.
I'm not sure what to do at this point.
Do you have a dual core system? If you do, you can only use 2 SODIMMs.