installation - 10.04 -> 10.10 - Problem after upgrade

So I just upgraded from 10.04 to 10.10 following this method, but now when I'm choosing Ubuntu in my GRUB, the screen with the Ubuntu logo appears for like 2 sec and then my screen just go in "idle" mode (the computer is still running) and I can't do anything else than doing a force restart of the machine.

I tried to launch the Recovery mode, I logged in and when I entered startx same thing happened.

I really have no idea of what the problem is, so if someone has one, please let me know.

(I don't know what other details I could give you, so just ask if you need something else)

EDIT

I tried the "Repair broken packages" option in the "Recovery mode" and I get the error that it can't remove fglrx. I tried:

sudo apt-get remove --purge xorg-driver-fglrx fglrx*

but it won't remove it. I get:

...
dpkg-divert: mismatch on package
  when removing 'diversion of /usr/lib/libGL.so.1.2 to /usr/lib/fglrx/libGL.so.1.2.xlibmesa by fglrx'
  found 'diversion of /usr/lib/libGL.so.1.2 to /usr/lib/fglrx/libGL.so.1.2.xlibmesa by xorg-driver-fglrx'
dpkg: error processing fglrx(--remove):
  subprocess installed post-removal script returned error exit status 2
Processing triggers for ureadahead ...
Errors were encountered while processing:
  fglrx
E: Sub-process /usr/bin/dpkg returned an error code (1)

So I guess this is my problem, how could I fix that?

(My video card is the Asus EAH4870)

So I finally found my solution thanks to these two sites: here and here.

The first one, with the response of Toon Macharis, helped me to resolve my dpkg:divert problem (need to modify the fglrx.postrm file), and then I was able to purge fglrx with the very good explanation of the second site.

Everything's working now.