What memory test did you run....if it was memtest86 then I would do as suggested and replace the memory cards.

Memory cards are the easiest parts of a computer to damage simply because they are in constant use and any spikes in the system or any static discharges can fry them.

Also Not all memory is compatable with all computersThis is the most common mistake that people and even techs make. Also it is best to all ways use the same manufacturer for each memory stick nstalled...while it is not so prevailent these days as before mismatched memory voltages can burn out sticks very easily.

There are some malware/virus that can cause memory failures ( memory handles failures). so make sure that your computer is clean and free from any malware/spyware/viruses.