PBA number is printed on a small label on your board. See AA, TA, SA or PBA numbers. The reason I'm asking for PBA# is that certain CPUs are only supported on certain PBA revisions. For same reason I asked for CPU model. See Important information on support of Intel® Xeon® Processor 5300 and Intel® Xeon® Processors 5400 and 5200 support.
The POST code LED translates to 0x21h: Initializing a chipset component. It's pretty early state during POST, before memory initialization. It would be very helpful if you can get the brand/model of your DIMMs and check if it's in the Tested memory list.
After checking the components compatibility, try one CPU in socket 1, and one DIMM in slot A1 first.