Take the SO-DIMMS out and carefully wipe the contacts with a new pink pencil eraser (not dried out) go with the grain of the pins one stroke per pin to make sure there is not oxide build up, then use a cotton swab with reagent grade 85% isopropyl alcohol.
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Try only installing two SO-DIMM and then try the other two.
Otherwise you’ll need to return the RAM to get another set.
Take the SO-DIMMS out and carefully wipe the contacts with a new pink pencil eraser (not dried out) go with the grain of the pins one stroke per pin to make sure there is not oxide build up, then use a cotton swab with reagent grade 85% isopropyl alcohol.
Otherwise you’ll need to return the RAM to get another set.