I think all of us would have been in this situation sometime or the other where we have a server whose RAID config has not been lost but the server is still not able to find the OS. It is indeed a strange situation because if the RAID config is not lost then the server should be able to see the Windows Partition, and if it’s able to see that then it should be able to boot off the files present there. This normally happens after a system board or HDD0 replacement. I found an explanation for this problem while working on such a situation with an IBM HW CE, he helped me fix the problem and I asked him for the link where this info is present. The link is here – http://www-947.ibm.com/support/entry/portal/docdisplay?lndocid=MIGR-5079636

It seems that Loading the defaults in Unified Extensible Firmware Interface (UEFI) deletes the Boot Order entries for any UEFI aware operating system. These entries are required to boot the operating system correctly. The workaround for this problem is given below.

The workaround is dependent upon the particular UEFI operating system. Refer to the UEFI operating system information for the actual file name and path used to boot that particular operating system.

For example, for Microsoft Windows Server 2008, the steps are as follows:

1) Power on the system, and, when prompted, press F1 to enter setup.
2) Select Boot Manager.
3) Select Boot from File.
4) Select the GUID Partition Tables (GPT) System Partition where you installed Microsoft Windows Server 2008. (This is mostly the first entry in the available list of options)
5) Select EFI.
6) Select Microsoft.
7) Select Boot.
8) Select bootmgfw.EFI.

The next question in my mind was that will the server boot up normally (without the need to follow the above steps) when it’s restarted or especially if it is powered off and then powered on, although I haven’t tested it myself but the answer should be yes, because the operating system is supposed to recreate the UEFI Boot Order Entry after we point it towards it once.