You might want to run memtest86+ (or the built-in equivalent from some OEMs like Dell), in my experience memory sticks sometimes go bad after being in use for a while.
Maybe just re-tuning the timing, if he's using high performance sticks. Because parts are hard to get by where I live, I usually stick 10+ years with a PC. With usage I found that I have to relax the timings a bit after some years.