Sounds like you having the same fun as a few people with Ubuntu and the ATI cards in 12.10
However there are ways around it.
First of all I would suggest you get your pc back to working order (albeit without full propriety ATI support) so you do not have to start in text mode again.
I would clean out any installs you have of the ATI drivers (so you can start again properly)
Open up a terminal (ctlr+alt+t) and insert the following command to cleanse your system of what has been installed so far:
sudo apt-get remove --purge fglrx-updates fglrx-amdcccle-updates
This should return your pc to its previous albeit open source state.
There is an issue many people have found with ATI's current driver which is affected by X-org changes with 12.10
I suggest you read this really excellent guide that Steven Myall did on ATI cards
Steven Myalls guide on Ask Ubuntu
This alerted me (I too have an ATI card which is a pain!) to the fact that I would have to downgrade my system slightly as I would also have to using this approach from Computers and You.
Computers and You guide to fixing ATI in Ubuntu 12.10
Personally I have to be honest here Michel and ask you to think about how much you need the proprietary drivers compared to the open source ones. For me for the amount I use them, it was not worth me doing this yet but I will do when I get a bit of time to mess around.However I do not do gaming or watch lots of videos.
However both sources I feel really go a long way to getting your system running Ubuntu with ATI drivers so if you want to get them working, these are the best ways.
Let us know how you get on.