I have a 2008 Mac Pro that randomly failed a couple of days ago. It stopped booting up except off of DVDs, curiously. When I did the Apple Hardware Test, the test did not return anything, but it did say that I have an error in the first slot of the DIMM riser B (the RAM board on the bottom) before I even ran the test. This is a second-hand computer, and I opened it up and realized that I actually have 6GB of RAM (2x2 + 2x1), not 4GB like the system detects! Evidently, the 1GB sticks don't work. They were on riser B. So I want to remove all the RAM from that riser, but the manual says that I need to put one RAM stick in the first slot of A and the second in the first slot of B if I want to use 2 RAM sticks. But it doesn't mention using 1 RAM stick at all. Can I use just 1 RAM stick or put both sticks on riser A in slots 1 and 2 safely?