I was having the same issue after uninstalling fcitx from Ubuntu 14.04.

I am giving you the main steps as I remember them.

A) Fix the boot loop first:

1. at login screen type Ctrl+Alt+F1 (or F2 .. F6)

2. you will enter a terminal in full black screen. From there you install fcitx AGAIN by

   sudo apt-get install fcitx
    
   

3. Go back to the normal login screen and now log in into your account

B) Uninstall fcitx cleanly:

1. Refer to this manual with Google translator.

2. Open terminal again and you only need following commands:

   sudo dpkg -l so*
   
   sudo apt-get purge sogoupinyin
   
   sudo apt-get purge fcitx
   
   sudo apt-get autoremove
    
   

3. Restart your computer.