Google search error message to enter captcha symbols to continue searching

Google search engine sometimes shows up this page where you need to enter captcha symbols to continue searching and the message goes on like this
To continue, enter characters below.
Our systems have detected unusual traffic from your computer network. This page checks to see if it's really you sending the requests and not a robot.

Troubleshooting (Try any one of them)

• Reboot the modem
• Reconnect the LAN if you are on a wired network
• Turn off the power and switch it on