no such disk error occured.
I tried to format and reinstall 12.04, the problem remained. I also repaired with boot-repair, the problem remained. http://paste.ubuntu.com/1224005/ is url of the details.
server is dell R710, the bios is set to uefi and disk is raid0 gpt. I typed commands in grub rescue:
- ls (hd0, gpt2), `no such partition' is shown
- set, `prefix=((null),gpt2)/grub' is shown
I don't know why /efi/ubuntu/grubx64.efi doesn't recognize disk. another strange thing is that there is only 1 file in /efi/ubuntu