unity - Ubuntu 14.04 desktop environment does not load

I am running (or at least trying to run) Ubuntu desktop 14.04.2 LTS on a Dell Optiplex 760 with intel Core2 Quad Q8300 CPU and an intel 4 series integrated graphics controller (uname -a :Linux systemname 3.13.0-53-generic #87-Ubuntu SMP Thu May 7 14:32:24 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux). Although I was able to load the desktop before, it fails to load now. What happens is that the purple screen with white ubuntu logo and the red over white dots below keeps on "loading" without changing, even after one hour of waiting time. I ran
apt-get update and apt-get dist-upgrade which both do not result in any issues. I triend some of the suggestions listed here, but did not get any results:

• When I try to run ccsm I get Gtkwarning: could not open display.


• dconf reset -f /org/compiz does not run with exit code 1 and an "error spawning command line"


• unity --replace has the following fatal error: compiz (core) - Fatal: Couldn't open display :0


• reinstalling ubuntu-desktop works flawlessly as does unity and lightdm


• mv ~/.config/dconf/user ~/.config/dconf/user.old does not help either

If more information is required I would gladly supply it. I can login and operate (as sudo) without any issues in tty1.

Update
I am able to run startx and switch to tty8 where I can load the unity desktop environment. Everything works except the header (menu) bar (i.e. no username, time, hplip icon, dropbox icon, network icon, ...) the launcher also does not auto-hide. tty7 keeps still doing the same thing as described above (purple loading screen). In tty8 I get a system program crash notification from signon-ui.

Update 2

I also tried using a boot from a live USB with Ubuntu 14.04, as suggested in the comments below. This works flawlessly, and I immediately get the menu bar with time and everything in tty7.

Update 3
Trying to upgrade to 14.10 does not work either it appears the changes cannot be calculated. A bug report was submitted.

Update 4
The upgrade to 14.10 succeeded after the bug report was marked as a duplicate. Uninstalling gnuplot allowed for 14.10 to be isntalled. The behaviour was even worse as the launcher nor menu bar were available in the startx desktop environment. However a subsequent upgrade to 15.04 resolved all the issues. Nonetheless, I accept the answer below. I did not verify if it works since I fixed my problem another way but the author claims this is the easiest answer to my original problem as stated here.