sometimes it shows up as 16 GB and sometimes it shows up only as 8 GB in both the BIOS and in Windows. I pulled out all the RAM and re-installed it the first time I noticed that only half the memory was showing up, and then it showed up as 16 GB. but then the next time I restarted it, it showed up as 8 GB again. I tried using memtest after mounting it to a disc, so I can see if it is the memory that is faulty, but could not successfully boot computer from disc. I think windows 7 OS disc, has a memory detector but I don't have the physical disc. Any suggestions? I am new to PCs.