Compaq D220 MT does not boot - Memory Refresh Failure or ???

[Franou]

Computer does not boot (HP/Compaq D220 MT/ Windows XP – SP2)
Disconnected everything except mouse, keyboard, and monitor
Computer cycles: HP logo, Windows XP logo, shuts down, HP logo, etc.
AMIBIOS v.1.09, released 11/14/2003
One beep: Memory Refresh Failure???
Motherboard: 335186-001
- Purchased a new RAM module from Crucial
Original was 256 MB, new is 512 MB, BIOS recognizes either and both
- Cannot boot from diskette (even made a new boot up diskette)
- Tested with two different sets of keyboard/mouse/monitor
- I have reset the BIOS
- RTC is OK
- BIOS Utility does not offer any diagnostic
- I have cleaned up the memory slots with air pressure and brush

How can I further diagnose the problem?
What could it be beside a dead MB?
THANKS!

Franou