I have an Early Mac Pro with 10 gigs of memory. The 2 from Apple and 8x2 gigs from OWC. For 4 months all was well but now RISER A slot 3 & 4 only show 1 gig each instead of 2 gigs. What would cause this? I ran the program Memtest V4.21 and it passed. Would this be a computer problem or a memory problem? Would Apple care as I didn't buy the extra memory from them 😕