My system was configured to dual boot Ubuntu 12.04.1 LTS and Windows 7. Today I got my hands on the MSDN release of Windows 8 and I installed it over my Windows 7. Now the computer just boots to Windows 8 directly without loading the GRUB screen.

So I followed the steps as suggested in: https://help.ubuntu.com/community/RecoveringUbuntuAfterInstallingWindows. Running this command:

    ls -l /dev/disk/by-label/

gives the following output:

    total 0
    lrwxrwxrwx 1 root root 10 Sep 11 07:51 Entertainment -> ../../sda2
    lrwxrwxrwx 1 root root 10 Sep 11 02:45 PENDRIVE -> ../../sdb1

Also fdisk -l command gives this as the output:

    Disk /dev/sda: 320.1 GB, 320072933376 bytes
    255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk identifier: 0x1246aa23

       Device Boot      Start         End      Blocks   Id  System
    /dev/sda1   *        2048   319582199   159790076    7  HPFS/NTFS/exFAT
    /dev/sda2       319582208   602906623   141662208    7  HPFS/NTFS/exFAT
    /dev/sda3       602908672   625135615    11113472   83  Linux

    Disk /dev/sdb: 1939 MB, 1939865600 bytes
    64 heads, 63 sectors/track, 939 cylinders, total 3788800 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk identifier: 0xc3072e18

       Device Boot      Start         End      Blocks   Id  System
    /dev/sdb1   *        2248     3788799     1893276    c  W95 FAT32 (LBA)

So I assume that I have to run this: sudo grub-install /dev/sda3 to get GRUB up and running. But I am getting this error:

    /usr/sbin/grub-probe: error: cannot find a device for /boot/grub (is /dev mounted?).

Can anyone please guide me in the right direction? The current Ubuntu installation is far too customized to my needs to lose it to a boot manager issue! Any help is much appreciated!