Wind 2000 Serv. Inaccessible_boot_device

Hi,
I have a computer with windows 2000 server loaded. I upgraded the server to service pack 4.
When I went to restart the computer I get the following error on the blue screen :
Inaccessible_boot_device
I did not archive the previous servicepack(if that matters). I tried running chkdsk, which did not help.I tried safe mode,last known good configuration. I do have many files I need on this drive.Is this drive recoverable?
Any help as to way and how this may have happened would be appreicated. Thank You