UNABLE to view our website while being plugged into our Nighthawk router

Hi,

I am having the strangest problem. I cannot access our website from our office.

I can see the website from my phone using the phone data and NOT the wireless.

I have restarted my dekstop computer.

I have rebooted the cable modem.

I have reset the Nighthawk router.

I pluged my desktop into the modem bypassing the router and I can see the website fine, no problem.

BUT when I pug back into the Nighthawk router no website.

It says the 

"The connection has timed out"
"The server at www.gospeltabernaclechurch.com is taking too long to respond."
"The site could be temporarily unavailable or too busy. Try again in a few moments."

Anybody got any idea what I can try?

Thanks

Leon