I recently reinstalled Ubuntu 12.04 LTS on a Dell Studio 1588 64-bit and ran into crashes as I was installing some software on the software centre.

Before this, I had display/screen problems that I needed to fix so I will briefly describe that in case it has any connection to the crashes. The problem was of screen crash/flickering (related to ATI Mobility Radeon HD 5400x) when trying to adjust brightness and so I followed guidance from an earlier chain (question 131967) to (a) use jockey to install fglrx update driver (deactivate experimental beta driver) and (b) edit grub to add acpi_backlight=vendor dell_laptop.backlight=0

The crashes that happened (twice, while software centre was just finishing installation in the background) was that all tabs (on open Firefox window) stayed open along with cursor control with mousepad but all menu bars disappeared completely along with the launcher and the keyboard also turned unresponsive. So there seemed to be no way to close windows or shut down the computer except for a forced hard shut down of the system using the start button. This is very similar to Questions #167540 and #298843, which seem to be closed.

Why is this happening? Is there some update or fix I need to make?

Thanks!