|You have to use the tp-link tl-wr740 router together with a separate modem. Is the modem working okay?. Connect you PC directly to the modem to check that it is connected to the internet.|
If you can't connect to the internet directly through the modem on it's own, it's the modem that's causing the problem, not the tp-link tl-wr740 router.
Try new cables for both the router and the modem.