[ALUG] main@lists.alug.org.uk problem with grub

Hi I have a problem I rebooted my desktop and its coming up with the following gave up waiting for root device alert /dev/disk/by-uuid-15e0064a.... does not exist. Dropping to shell. Now my /boot is on a raid partition /root and the others are on lvm2 When I look in the lvm in the shell it suggests that the lvm is inactive. I have tried using a live disk to rebuild grub but I must be missing the correct command fu. Anyone got any suggestions Ben