We have a Dell poweredge 2970 with 4 drives. Someone claimed to have shutdown the server and no one mention of any hardware changes. But when we tried to start we have a Memory error saying is not optimal and also 2 logical drives failed and the server is no more booting.
Call Dell support, explain the situation. If this is a raid-5, a re-tag might work, they'll also take care of the memory issue - those are fairly easy to handle.
It might possibly be that the RAID controller battery is dead, and the configuration has been lost. Some poweredge systems I've worked with in the can reload the configuration from disk when that happens, but I've not seen that option for some time.
Firstly, you need to be prepared to rebuild the system from your backups.
Is the server covered by a warranty? If so, you should call Dell before you do anything.
Do you have any physical disk failures? Does the physical disk configuration look right?
Bear in mind when looking at the RAID controller configuration, one incorrect keypress could potentially ruin any chance you have of booting the system again.