Ubuntu – Lost unity taskbars and window frames after upgrading from 12.04 LTS on a Dell Precision m4600 nVidia

I just upgraded from 12.04 LTS. The upgrade went fine until the moment, while still installing packages, all the unity taskbars and window frames went away. I could do nothing more but observe the installation progress (the only app I had running was Chrome but it hanged, and because of lack of taskbars I couldn't restart it). But installation finished successfully and it asked for reboot. After rebooting, it booted into some low-res mode, displayed a message box that it can't detect my video drivers correctly and apparently I couldn't do anything – there were no reaction to mouse nor keyboard. Oh.

However, I noticed in the logs that while booting, it started that bumblebee optimus thing. I had optimus disabled, so I went to bios and enabled it. I also managed to get into text console (framebuffer) and changed grub settings to boot straight into text mode. Now I tried starting X server manually (startx) and it showed me the high-res desktop, started two apps that I had in autostart, mouse and keyboard were fine. But no taskbars and no window frames. The screen resolution was fine (1920×1080) and looked like nvidia drivers booted properly.

The next thing I tried was uninstalling nvidia-current-updates, uninstalling bumblebee-nvidia, and setting xorg.conf driver to vesa and then nouveau. In both cases, I got low-res desktop with no damn taskbars nor frames. So then I installed only nvidia-current-updates (installation went fine) – I got back nvidia drivers working (logs and splash screen confirmed it), high-res desktop, but of course still with no unity taskbars.

The last thing I tried was removing .compiz and .config/compiz directories from my home folder, as I read such advice on the Internet. Didn't work. Also creating a fresh user account and starting x from there – showed only empty desktop, no taskbars.

Now I'm stuck. Seems the damn thing doesn't work at all. I have to get it somehow working by Monday. Please help me what can I do to:

1. fix it
2. debug it and fix it
3. workaround it, at least so I can make some work while still trying to fix it later – I was thinking of installing a different graphic shell, but I don't know which are usable with ubuntu
4. downgrade to ubuntu 12.04 (but really don't want to do that)

My hardware:
Dell Precision m4600
i7 Core Quad, 24 GB RAM
nVidia quadro 1000M

Ubuntu installed kernel 3.5.0-17.

Thanks a lot,
Piotr