Originally Posted by Dagwyn
Question: is all lost?
No, seriously, it depends from what happened during power going down. From what you describe something has overwritten the MBR / partition table.
I'd suggest the following:
dd if=/dev/sdb of=/some/place/on/a/different/disk/sdb.mbr count=1 bs=512
That will preserve the original MBR of /dev/sdb.
Then call "fdisk /dev/sdb" and create a partition of the type "linux LVM" on the whole disk (fdisk will propose the appropriate cylinder numbers). Write the new partition table and cross your fingers during reboot.
The validity of the data on the disk will depend from how far the process of overwriting things had run during that crash.
Need I stress the point that you best clone the entire drive if it contains valuable data before you start experimenting? Good luck...