To enable pings (ICMP echo request/response) follow the steps below.
Login to the router using your web browser. (Type http://192.168.1.1 (default is 192.168.1.1) in the address field of your browser, and then press Enter).
The default username is "admin" and the default password is "admin".
Once logged in at the top of the page you will have a set of tabs, click on "Advanced". Then select "Advanced Security" from the menu on the left.
Tick "Allow incoming ICMP ping" and "Apply" to apply the setting.
The above procedure is documented in the install guide (pdf, 4 MB) on page 33, this includes images of the web interface.