I am new to Linux using Ubuntu 12.04 LTS but I would have taken all of the steps that you have taken and I would have expected the problem to be solved.
Assuming that you have a backup of /home, why not do a complete reinstall of the system and then restore your /home from backup?
Alternatively, you could create a new account for yourself with a new user ID and see if that works. If this action is successful, you can copy your home files to this new account.
I am content to stay with 12.04 LTS until the new LTS comes out as I do not like to cope with change too often.
PS I have dabbled with several Linux distros recently and the one that impresses me for ease of use and robustness (and automatic wireless configuration) is PCLINUXOS.