If you are having trouble installing LiteLoader, check the following things:
Check that you have the
latest installer, if you are unsure then re-download the installer from the
download page.
Check that your Java installation (JRE) is up-to-date. If you get a message saying that the installer “cannot be started” or “cannot be launched”, check that you have Java 7 or later installed.
Make sure you are using the
Official Mojang Launcher. If you are using a third-party launcher then you should follow the appropriate steps in the
installation trail for third-party launchers. If you are using a “cracked” launcher, then you are on your own.
If you are using the exe installer on windows and are having difficulty, try using the jar installer.
If the installer will not launch and you are sure your Java installation is up-to-date, ensure that over-zealous anti-virus software isn't blocking the installation.
If you are still having problems after having tried all of the above, then you should post on the forum thread. Provide as much detail as possible and mention that you have already tried all the steps mentioned on this page.