I have a Small Business Server 2003 which crashed the other day. When it rebooted the BIOS said the system memory had changed. The server had a backup 256Mb of RAM which allowed the server to reboot but it ran very slowly.
I assumed the RAM chip had failed and as they work in pairs I replaced both sticks. The Server boots and get to the logon screen. All users can logon from their PCs and use the files and exchange. The Server seems faster as we upgraded thew amount of RAM.
However, if you try to logon to the server console (at the Server or RDP) the server hangs and users stop working.