Another way to do it (if you are willing to lose a lot of data from your modpacks) is delete the entire .techniclauncher file and reboot the launcher (simply by clicking login after having deleted folder). This is located in %appdata% roaming folder, usually under the .minecraft folder. This is what I did because only Tekkit was updating and the others were not.
If you have world saves that you wish to keep, just copy/cut the "saves" folders and put them somewhere else. Then, after deleting the .techniclauncher folder and rebooting the launcher, put the saves back in.
I hope this helps. It is the most surefire way I know to get it working again. It might be more work than other methods, wth dragging files you want to keep around, but it should work well. Thanks!