So I was installing W3 Total Cache to my multi network wordpress site.
Suddenly while activating the plugin I started to get 500 Error for all pages in my site. I was not able to login also to my site.
I searched in Google and found many solutions Some suggested deleting the W3 cache plugin folder from the plugins directory. Some suggested restore of old backups.
I looked into the log of error in my Cpanel and found its due to wrong .htaccess file.