When seating the bottom RAM chip you may have to apply a little extra side force to get it to seat properly. I put in the new RAM and just got a beeping sound upon starting. I then put the old RAM back in and got the same result.
Here is the solution I found on the Apple discussion board.
"Take a small flat head screwdriver and after you put the memory in slot 0, put the screwdriver between the top of the mac mini and the memory then turn the screwdriver a little to exert pressure on the memory into the slot. Do it on both sides of the memory."
This worked for me.
