This was probably caused by fixes and features backported from newer kernels.
In GRUB menu, select Advanced options for Ubuntu, choose the last kernel that worked (not recovery mode).
Now you can:
- Remove new kernel and keep using old one, making your system vulnerable to old kernel exploits
- Install newer kernel, for which these fixes were made
Easiest way to install new kernel is to download it from kernel.ubuntu.com and install it using
First, select the version you want (preferably the newest non-rc one,
utopic kernels will work for 14.04 too), then download 3 files:
Replace architecture with i386 if you use 32-bit Ubuntu, or amd64 if you use 64-bit one (it has nothing to do with CPU manufacturer!).
Move these files to separate directory, open your terminal,
cd to that directory and then run this command:
sudo dpkg -i *.deb
dpkg finishes, you can reboot, and ensure that you are running the kernel you've installed:
Linux m132 x.xx.x #1 SMP Tue Jun 10 00:45:23 CEST 2014 x86_64 x86_64 x86_64 GNU/Linux
Remember, you'll have to update kernel manually now, because Software Updates will only install 3.13 patches, as the kernel version never changes after Ubuntu release.
If it still doesn't work, uninstall the kernel you've installed with
sudo apt-get purge linux-headers-3.13.0-24 linux-headers-3.13.0-24-generic linux-image-3.13.0-24-generic
sudo apt-get purge linux-image-extra-3.13.0-24-generic
Replace 3.13.0-24 with version you want to uninstall (or press Tab key to list installed ones). Second command may throw an error as there's no
linux-image-extra for some kernels.
PS: Please, follow these instructions to make a bug report for that faulty kernel, so they can fix it for others :)