[update 2018]
The plugin presented in the article below is no longer available. For more details about How can you create a 404 page, How you can identify if the site visitors access pages 404 (non -existent) and How can you correct these issues, consult Google Console (gives you reports on your website's health) and the item dedicated to this topic on WordPress.org (https://codex.wordpress.org/Creating_an_Error_404_Page) )
When a reader of yours does not find one or more page required on site, means that your blog has become ill with Error 404: Page not found. In the best case, it may be some pages imagined by users, who have never existed in your blog.

But most of the time it is about corrupt links or pages that had displays at a time but which, because of some Site changes or some fall, now displays error 404. In these situations it is necessary to repair the "Page Not Found" errors as possible, considering that they can have a rather unpleasant impact on the site indexation in Google Search.
To check if the equipment blog suffers from such errors 404 and to repair these errors if necessary, you have a handy plugin WordPress, namely TentBlogger 404 Repair.
TentBlogger 404 Repair check all requests for display of the pages of your blog made by readers or by search engines, and announces when requests result in errors 404: Page not Found. The plugin displays the corrupt links so you can quickly identify the errors and then repair. Once the errors are repaired, yes click on Repaired next to them so that the plugin does not further display the error.

Download TentBlogger 404 Repair WordPress Plugin
To check if the plugin works correctly on your site, after installing it requires displaying a Non -existent pages on the blog.

The plugin will register the failed request and display the wrong link in dashboard.
STEALTH SETTINGS – Find and repair 404 errors (Page not found) in your WordPress blog
Error resolution 404 and 403: Reinstal Browser+ Addon VPN or change from https to http and if it does not work it means the site has been erased. PS: For more details look for the respective information on the net. (valid only for beginners)