Ok, this is the weirdest problem I have ever encountered. My system initially had 256MB PC2700, and I recently got another 256MB stick to upgrade to 512MB. After putting the memory in, the computer booted just fine, but still only thought it had 256MB. I figured it just wasn't seated correctly, so I tried to reseat it...same problem. Okay, so now I swap the places of each of the DIMMs and still the same problem. If I use just one at a time, the computer boots up fine, so I know the memory is good. Now here's where it gets really weird. When both of them are in, if I go in SiSoft Sandra or cpu-z, the computer KNOWS that there are two DIMMS, it even has the name strings for both of them! I tried removing one to make sure this wasn't a fluke, and sure enough, the next time one was missing from the list. At this point, I have run out of ideas for getting all the RAM to work. I tried resetting the CMOS, and even upgraded the BIOS trying to solve this. Does anyone know what's going on? btw the mobo is an Abit KD-7 RAID (Via KT400 chipset)

The two sticks are okay by their selves but when together it does not read correctly. Incompatible Ram......

Yeah, I was beginning to think that may be the problem, even though I thought those days were long over.