We have 2 optiplex gx620 computers. Both a running windows 7 pro. For some reason, I'm only able to put in 3 Gb of memory. When I try to add the 4th Gb, the computers won't boot and give a beeping sound with the on/off light yellow. This happens with both computers. The problem doesn't seem to be from the memory sticks since switching the sticks doesn't cause a problem. It's only when trying to go up to 4 Gb that the problem occurs. All memory sticks are the same type - dell - low density - 1024MB PC2-6400 DDR2 RAM
Help appreciated.