I can't remember where, but I've see something like your problem. What I remember is solution involves /etc/fstab file.
Maybe this link can help you: https://help.ubuntu.com/community/Fstab
Here is my fstab, just in case:
# /etc/fstab: static file system information.
# Use 'blkid -o value -s UUID' to print the universally unique identifier
# for a device; this may be used with UUID= as a more robust way to name
# devices that works even if disks are added and removed. See fstab(5).
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc defaults 0 0
# / was on /dev/sda5 during installation
UUID=c105cdce-299b-4972-83a7-540d75acfb8c / ext4 errors=remount-ro 0 1
# /home was on /dev/sda6 during installation
UUID=a28726f9-83ea-482c-8ff9-aa791f693762 /home ext4 defaults 0 2
# swap was on /dev/sda1 during installation
UUID=fd6eb774-043b-4203-a797-a91f666989fa none swap sw 0 0
/dev/scd0 /media/cdrom0 udf,iso9660 user,noauto,exec,utf8 0 0