Purab

I am looking into issue

You should use the following command on linux box from blocking the ip address.
iptables -A INPUT -s 198.154.62.21 -j DROP

above commands will only work on linux boxes.

you can add the second sidebar using following URL:
I found really informative.

[link removed]

I faced similier issue. I just deleted the w3 cache then removed the cache directory from wp-content folder and reinstalled the w3 cahce plugin and configured again..That works for me perfectly.

This link found me helpful. I deactvated all plugin but still issue not solved.

I deleted the cache from wp-content folder using following command.
rm -rf w3tc

This solved my issue.