There are lot many post i can see in the wordpress forum discussing about images are not showing in the Media library wordpress 4.3 and same issue was happened with me.

I got the solution for this issue. Follow below steps to fix this.

1. Open your websites file via shell or file access to the server (FTP).

2. Go to directory called wp-includes.

3. Open taxonomy.php file in your favourite text editor.

4. Replace line number 4448 with the below line :

wp_schedule_single_event( time() + MINUTE_IN_SECONDS, ‘wp_batch_split_terms’ );

5. Save it and refresh your post page. Yeah !! It started showing images again.

For full description you can go to this link : https://wordpress.org/support/topic/high-cpu-load-after-update-to-v43?replies=17#post-7330770

 

If this doesn’t fix your problem than i would recommend to follow below steps to debug problem :

Step 1: Disable all of your plugins and test to see if your media library is working. Now test to see if your Media Library is now functioning: (If it is working then go through and activate each plugin one at a time and see which one it is breaking your media library, then do not use it. Likewise if this does not solve the problem go to the next step)

Step 2: Log into your admin panel.

Step 3: Go to Settings > Media

Step 4: In the first writable field (Store uploads in this folder) it will state that the Default is wp-content/uploads but, it will not register this as “True”.

Step 5: Type “wp-content/uploads” within the field. (Also, make sure that “Full URL path to files” is blank.)

Step 6: Click, Save Changes. Now test to see if your Media Library is now functioning if not go to the next steps:

Step 7: Open up your File Transfer Protocol or (FTP).

Step 8: Go to your wp-content section. This will be listed within your sever at YOUR-SITE.COM/wp-content/

Step 9: Right click or highlight your “uploads” folder. If you do not have one then create one and test to see if your Media Library is now functioning. You need to have a folder here at YOUR-SITE.COM/wp-content/uploads/

Step 10: If you have an uploads folder already, select its “File Permissions”.

Step 11: Set the Numeric Value to 755 or 777 (777 can present a security risk see details below). Now test to see if your Media Library is now functioning if not go to the next steps:

Step 12: Go back into Go to Settings > Media

Step 13: Uncheck “Organize my uploads into month- and year-based folders”.

Step 14: Click, Save Changes. Now test to see if your Media Library is now functioning if not go to the next steps:

Step 15: If your Media Library is still not working there is only one more step that I can fathom. Go back into your File Transfer Protocol or (FTP).

Step 16: Right click or highlight your “wp-content” folder.

Step 17: Select “File Permissions”.

Step 18: Set the Numeric Value to 777. Now test to see if your Media Library is now functioning and hopefully it is by now. Please note if your website is still down, it could potentially one of two things. The first being a plugin that you chose or created. Most free plugins do not take in consideration that your site matters. It is a pain, but do some research on the person who uploaded the theme and be sure that you check their reviews. The second reason could be due to some of your folder permissions — they might have been lost during a host transfer.

Step 19: If these solutions don’t work double check your .htaccess file and make sure this file matches with the theme you have installed on your site. Sometimes if this is not setup correctly it will re-write the path of the uploaded image. This is something you will have to investigate on your own and you can click here to fix your WordPress htaccess file.

Try re-installing WordPress again, and re-importing your themes and plugins. If these solutions still do not work, feel free to comment below. I will definitely try to help you.

Be Cautious: Doing some of these steps could potentially open up your website to a security breach, mainly by changing the directories to 777 if you went all the way to step 19 to get your Media Library to function. Don’t worry to much; if you had that much trouble getting it to work your server obviously has a great deal of security within it.