@Gillian 

Hi, please tell us more details then we can help.

What's the model number and hardware version of your device? What's the light status on it?  Where did you see the message 'can't connect to internet'.

Does it work fine before? How do you connect the modem to the internet source?  With the telephone cable or Ethernet cable?

@Stella.Q 

Hi,

Model is TD-VG3631

Power light comes on. WiFi light flashes

When I try to connect to the internet device shows as connected to the modem, but not to internet.

Yes, it was working fine early in the day.

Connected with Ethernet cable.

Thanks

@Gillian 

Hi, thanks for the info. 

You can connect that Ethernet cable to the computer directly, if there is no internet, you should contact the ISP to check the line. If the internet is working, you can restart the modem and refer to the instruction below to reconfigure it (EWAN means the wireless router mode, go to Network--EWAN to do the settings). 

https://www.tp-link.com/support/faq/543/

Note: during the configuration, you may need to put in some parameters such as username&password or VLAN ID from the ISP.