@leo33 

Check Internet port settings to be sure that everything is properly configured:

Does your ISP use an MAC address protection ? Maybe MAC Clone should be configured - just consult with your ISP.

@leo33 

Kindly try Ivaylo's suggestions, and see if any of those will help.

Just to add, when you connect the C80 to the ISP modem, will it be able to get a WAN IP address via PPPoE now? What is it? Please show us the screenshot of the Status page on the C80. If there is a WAN IP address, please try to change the DNS Server on the internet to 8.8.8.8 and 8.8.4.4, then reboot the modem and the C80, check if the internet light will become green.

BTW, who is your ISP?

@Kevin_Z thanks for Replying to my post. Well my ISP provider basically has direct Fiber line from Connect services which is the main company located in Karachi. The main fiber line goes through the modem which the ISP has in shop & then the ethernet wire in inserted in Dlink port switches through which 1 ethernet wire is coming to my room in which is inserted in the WAN Port of the router. Also the connection is Protected on the ISP side by a Mac address which is entered by the ISP when the router is first connected to the ISP internet through the ethernet wire. Currently am using a very small Tplink router N300 which to my amazement still works & that is 4 years old.

@Ivaylo Thanks for replying to my Post. Well that I didn't check bro. But earlier when the tplink router was configured for the first time out of the box by the ISP it worked perfectly at home no issue at all. But just after the update the issue happened. But I will check with ISP again today & try to post a screen shot too. 

@leo33 

Thank you very much for getting back with the valued info.

Just to confirm, what is the model number of the N300 router? Can you please show me the Status page, including the WAN info?

When it is convenient, please try to connect the C80 back to the network, try to choose the same WAN connection type as on the N300, then confirm again if it connects. Show us the Status page on the C80 as well, no matter it is working or not.

We will escalate this case to the engineers, who will help you solve the issue via email later if all these suggestions don't help.

Have a nice day.
 

@leo33 

If the issue persists after the talks with your ISP you may hard reset the router and re-configure from scratch - this does help in many cases after FW upgrade.

@Kevin_Z  I just spoke with my ISP. He told me that the issue with C80 after firmware update is that it doesn't pick the ip address of the ISP at all. If it picks the ip address of the ISP than its Mac address would be saved automatically in the ISP servers..

I'm attaching a pic of the status page of the TP link router that is working currently. 

Currently I can't my self connect the C80 back in because if I change the router the routers max address will be blocked immediately. Because the old routers MAC address has to be cleared first. Also I did ask my ISP about changing the DNS server in my C80 like you said but he is telling me that the main ISP has already made the configuration changes at there side with the same settings of DNS servers & on user side it is Set for Auto configuration only. 

Currently my ISP person is out in the field. Thanks for the rapid response. 

@Kevin_Z WAN INFO of the router that is working 

@Ivaylo How to Hard Reset??? Seems like the logical solution to me at the mom. Had a call with the ISP & he said that the problem with the C80 is that it isn't picking up the COMPANY'S ip address. The C80 picked the ip address of the ISP earlier before firmware update & the same settings were done from scratch in C80 1 time after firmware update & 3 times after resetting the router by holding the reset button on the back of the router but it just doesn't work. Currently C80 is installed in access point mode & working. But I want to use it directly in router mode which I am unable to do so. 

Please help me. Thanks.

If you already have reset the device after FW upgrade (by the button on the back), re-configured from scratch and it still doesn't connect, then that won't help either. In that case follow Kevin's directions.