You'll have to change your permissions back to what they were. Many system programs have specific permissions requirements, and changing permissions outside of your home directory isn't a good idea unless you specifically know that it's safe to do.
If you changed a bunch of permissions and don't know their original values, you're looking at a reinstall. Fixing a large number of permissions would be really difficult to do correctly.
If you aren't able to use the
chown commands due to your messed up permissions, boot into the live CD, mount your hard drive, and fix the permissions from there.