Yes. Assuming the PPA hasn't borked essential components of your system (like network connection, package management, and boot) it should be possible to restore your system to mainline Ubuntu packages.
Getting into a repair environment
First, get to a command-line. If your system is still usable enough to login and use an Ubuntu session, launch 'Terminal'. If not, press Ctrl-Alt-F1 (Ctrl-Alt-Fn-F1 if you have media keys), and login to the text prompt.
Resolving package inconsistencies, if any
Now. First, finish any incomplete updates that may have been interrupted.
sudo dpkg --configure -a
If this repairs anything, it's possible no further repairs will be necessary; simply skip to the Finishing up step below. If nothing is repaired, the package integrity of your system is good, and PPAs may indeed be resposible.
Installing a PPA removal tool
sudo apt-get install ppa-purge
If you're using Ubuntu 10.04, you need to add lucid-backports to your software sources.
Removing potentially damaging PPAs
And then uninstall PPAs from your system like so, replacing
ricotz/testing with the PPA you want to remove:
sudo ppa-purge ppa:ricotz/testing
(If you do not know what PPAs you have installed, you can check with
cat /etc/apt/sources.list /etc/apt/sources.list.d/*.list | grep ppa. The PPA names correspond the unique portion of the URLs, such as
Finally, update your system and restart.
sudo apt-get update && sudo apt-get upgrade
sudo shutdown -r now
Hopefully you will reboot into a fixed Ubuntu.