dellpower edge sc1420 not detecting memory

hi all i have a dell poweredge sc1420 when i power it on give six beep in order 1-3-2 and indicator light A-green B-orange C-green D-orange.

the system have 2 gb ram.
1gb in dimm1 and another in dimm 2. i try to start the system with only 1 module. still doesn’t work try to put a known working module in dimm 1 still doesn’t work.

can anybody help