1.Checking for Corrupt .htaccess File
The first thing you should do when troubleshooting the internal server error in WordPress is check for the corrupted .htaccess file. You can do so by renaming your main .htaccess file to something like .htaccess_old. To rename the .htaccess file, you will need to login to your site using the FTP. Once you are in, the .htaccess file will be located in the same directory where you will see folders like wp-content, wp-admin, and wp-includes.
Once you have renamed the .htaccess file, try loading your site to see if this solved the problem. If it did, then give yourself a pat on the back because you fixed the internal server error. Before you move on with other things, make sure that you go to Settings » Permalinks and click the save button. This will generate a new .htaccess file for you with proper rewrite rules to ensure that your post pages do not return a 404.
2.Increasing the PHP Memory Limit
- Create a blank text file called php.ini
- Paste this code in there: memory=64MB
- Save the file
- Upload it into your /wp-admin/ folder using FTP
3.Deactivate all Plugins
4.Re-uploading Core Files
re-uploading the wp-admin and wp-includes folder from a fresh WordPress install.
