Honestly, what you should do is call a Linux pro - this may disappoint you since you'll have to pay for it but I believe your skills are not enough.
This looks like a serious problem which handled wrong might ruin every piece of data you've got.
Done correctly - well, everything except broken hardware can be fixed.
Of course it depends on the server, what's it used for, how many are depending on it?
If you want to try yourself, here's my "analysis":
1) At least one partition on one disk - but probably more - are faulty.
It could be a physically damaged hard disk or just a corrupt filesystem, impossible to tell by now.
One reason for a corrupt filesystem is an abrupt power down.
On the other hand, a faulty system might cause a powerdown.
2) The system seems to boot up from wrong disk/partition.
This can be because one disk is physically damaged and therefore not seen.
It could also be that the disks are numbered in a different order - that happens with anything but IDE-drives (AFAIK)
In order to help you along we need the following:
Post the systems /etc/fstab.
If you can't read that file write down what you remember/know of the partitioning & mounting scheme, including info about what filesystem is used.
Information about bootloader - lilo or grub?
Post bootloaders config file.
try to repare a filesystem if you don't know what you are doing! (Personally, I learned that the hard way, ruined a very pretty girls disk completely
Or you could simply reinstall.
Depends of course on what it's used for, if you can set it up again with the used apps, and if you know where users data is. If the system is properly setup you can remove the system without touching users data.
Edit: I forgot something very important:
Don't do anything from the system itself! Shut it down if it's running and don't start it again!
Boot from a live-cd, then check out your disks & partitions.
Mount the partitions you need read-only!
Here are a few commands:
# fdisk -l (shows the disks & partitions)
# mount /dev/sda1 /mnt/sda1 -o ro (mounts /dev/sda1 readonly on directory /mnt/sda1)