Not really sure what your problem is.

Let me ask this:

did you at any stage edit the file:

_plugins_admin.class.php

if you did, you should download b2evo version 4.0.5 and find the original file located at:

inc/plugins/model/_plugins_admin.class.php 

copy that file and paste it in the directory of your site at the same location.

when you get the error:

Fatal error: Call to undefined function token_get_all() in /home/public_html/inc/plugins/model/_plugins_admin.class.php on line 438

...then it means that some file is requesting a function which can not be found or does not exist.

If you can say which plugin or file you edited then maybe we can find a solution.

the problem is came when i want to install plugin: Who's online Widget.
and now is not working to edit no one of plugin. i get error.

Then copy the _whosonline.plugin.php file from a fresh install, go to your site/plugins/_whosonline.plugin.php delete it from your directory and replace it by with a new file. What is your site url?