I have a Mac Pro 1.1 which won't boot properly - it's unstable. The lower memory board shows a red light opposite 03A3, which seems to correspond to DIMM2. I took out the two 1Gb RAMs that were in DIMM 1 and 2 and put in two 512Mb from the upper memory board. Same red light comes on. Does this mean a fault with the actual memory board or riser or what? How do I fix this? Thanks for help.