Search for Linux image
# apt-cache search linux-image

Pick your image version. For example I choose 3.13.0-93-generic image. then download and install it...
apt-get install linux-image-3.13.0-93-generic

You may also download Linux hearders ...
apt-get install linux-headers-3.13.0-93-generic

Fix and Check grub list file at /boot/grub/menu.lst before restart.