Question: I run Ubuntu 12.04.4 LTS 32 bit version and recently took the option to take the HWE upgrade from Update Manager. Now either the computer freezes or I go into a low graphic mode similar to the Terminal. I believe this is because I have an old Nvidia FX5600 graphic card. If I run 3.13.0-32-generic in recovery mode I can use my computer. My question is can I reverse out the HWE upgrade or will I have to reinstall the OS from scratch using the original CD?

Answer: 
The core problem is that the HWE update doesn't install the headers for the new kernel. These headers are necessary for the NVidia driver to build its kernel module. To fix it, simply install the linux headers and then reinstall whatever nvidia driver you're using:

```
sudo apt-get install linux-headers-generic-lts-trusty

```

**Note:** this is for Ubuntu 12.04.5, if you're using a later release, it's going to be `linux-headers-generic-lts-RELEASENAME`.

Then when you reinstall the nvidia driver and reboot, you should be fine once again.
I just had this same issue while upgrading my HWE on 12.04.

After upgrading, everything worked fine for a few minutes and then the screen went distorted and pixelated. 

What I had to do was hard restart the PC and enter into recovery mode on reboot. I enabled networking and then dropped to the root shell. There I apt-get updated/upgraded and then rebooted again into normal mode. No icons loaded this time and I rebooted again. Another reboot appeared to fix the problem.

It looks like it was caused by a NVIDIA driver Bug [Screen freeze and garbled after resume from suspend](https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-331/+bug/1210077)

Hope this helps someone.