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#11
Depending on certain builds, they might have had minor settings. As for expandable, it is. However, what most normal users don't realize is you just do go 'buy ram and stick it in'. You have to buy specific ram for a specific system. In some cases, you may have to go into the BIOS and make some minor checks or changes to assure that it recognizes the change in the system. Dells normally do a BIOS alert warning stating exactly that for that reason, to make sure that the user is aware a change has been made and to check bios in case this was not the case.
As for re-seating, yes, take them out, used compressed air or something that will blow a puff of air over the ram slots and over the ram, do not touch the ram contacts directly. Then put them back in. Sometimes with memory upgrades, especially in systems that have been in operation long enough for the system to have dust within, can have contacts blocked by dust, which could also account for issues.
I would recommend just pulling the ram out... Do a light clean and put it in, go back into the bios and make sure it SEES 8 gigs.