Let me tell you how I fixed a similar issue I had. This should help you to fix yours too.
I have dual booting Win7 and Ubuntu12.04 which was working perfectly fine. I accidently deleted the extended logical volume(partition 4) when in Windows and there is no boot now with grub rescue prompt after I shutdown Windows.
Configuration of my Single disk with 6 partitions:
partition 1= primary partition;
partition 2= primary partition = Win7;
partition 3= logical drive in extended partition;
partition 4= logical drive in extended partition;
partition 5= primary partition = Unbuntu12.04;
partition 6= primary partition = swap
So now the partition number that grub is searching for a bootfile is (hd0,msdos7) whereas the bootfile is actually located at (hd0,msdos6) due to the partition delete.
You can check this by the command "set" at grub rescue prompt. This shows me that the partition set to boot is (hd0,msdos7).
To show all partitions use "ls":
grub rescue> ls
(hd0,msdos7) (hd0,msdos6) (hd0,msdos5) (hd0,msdos2) (hd0,msdos1)
Then check for bootfile in each partition:
grub rescue> ls (hd0,msdos7)/boot ... unknown filesystem
grub rescue> ls (hd0,msdos5)/boot ... unknown filesystem
grub rescue> ls (hd0,msdos6)/boot ... grub ... initrd.img-2.6.32-33-generic ... vmlinuz-2.6.32-33-generic.......
So now we know the actual bootfile is at (hd0,msdos6).
Now set this bootlocation temporarily in bootloader and boot into the OS:
grub rescue> set root=(hd0,msdos6)
grub rescue> set prefix=(hd0,msdos6)/boot/grub
grub rescue> insmod normal
grub rescue> normal
This boots us directly into the OS.
Once I booted into Windows, I downloaded and used the free windows program AOMEI Partition Assistant Standard Edition 5.5 to restore the deleted volume. After that I restarted Windows all works fine like nothing happened.
Something funny with Windows7 here. Apparently diskpart thinks the primary partitions 5 and 6 are logical drives (diskpart>select disk 0 >list partition) whereas Disk Management shows the same partitions of Ubuntu as primary partitions.