Re: Missing /dev /sys /proc
The first thing I would do would be to run a file system check in the / partition, and that will probably fix it.
First you'll need to boot your Ubuntu Live CD, or if you installed by USB then use that, or you could use a different Ubuntu or other Linux operating system providing it has ext4 support.
Once your Live CD or other operating system has booted, open a terminal and run e2fsck like this,
Where: /dev/sda1 is your / partition, replace with a different partition number if needed,
sudo e2fsck -C0 -p -f -v /dev/sda1
Where: /dev/sda12 contains an ext series file system.
Note: the 'C' must be in upper case, the 0 is a zero,
-p means to 'preen' the file system meaning to automatically fix most problems but not if it means moving files to the lost+found, if the damage is too severe it will give you a report instead advising what to do next, (rather than just automatically moving your files).
-f stands for 'force', (run the check anyway even if the file system might not really need it).
-v is for 'verbose', (tell you what it's doing/has done).
e2fsck is the program for checking and repairing ext series file systems.
Ubuntu user since 2004 (Warty Warthog)