cannot mount a partition (error 990)

["jdf [zionarea.org]" <zionarea@xxxxxxx>]

Hi,

I'm very annoyed. After a crash, my working partition (containing
things about years) cannot be remounted anymore.
fsck does nothing at all.

Error is, according to dmesg:

XFS mounting filesystem hdxy
XFS: log has mismatched uuid - can't recover
XFS: failed to find log head
XFS: log mount/recovery failed: error 990
XFS: log mount failed

I tried xfs_repair -n /dev/hdxy

the result is:

xfs_repair: can't determine device size

What should I do in order not to loose all my data ? I really hope
there's a solution even if I got older data. Unfortunately, I didn't
backup anything.

Please help me !