GRUB can't access my linux partition?

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http://askubuntu.com – Until now I had 2 NTFS partitions on my harddrive. Now I wanted to install Ubuntu 12.04, so i freed 100GB from the end of my harddrive, created a new ext4 partition, and installed Ubuntu 12.04 on it. That's how my partitions table look: /dev/sda1 - 98.81GB NTFS /dev/sda5 - 732.71GB NTFS /dev/sda6 - 100.00GB EXT4 The GRUB has written the data to the harddrive's MBR, however it seems that it can't access the /dev/sda6/ partition. IT boots up to resuce mode, and when I type ls I can only see (hd0) and (hd0,ms-dos). Is it because the boot files are on an extended partition? If so, how can I (HowTos)