To connect to the TP-LINK W8980, set your computer's (laptop's) IP manually to 192.168.1.2, mask to 255.255.255.0, and gateway to 192.168.1.1 for the computer's eth0 interface. Then try to access the router via 192.168.1.1.
Setting IP, mask, and gateway varies from one system to another. In general though in the upper right or lower right of ones screen there will be a network icon. Left or right click to get menu under which you select network settings or something similar. Select options for your wired interface and then IPv4. Set method to manual and input settings as above. You can get here too from the control/system panel by selecting the network icon there.
Alternatively from the linux command line something like this as root or use sudo:
ip address add 192.168.1.2/24 dev eth0
route add default gw 192.168.1.1
Check your OS, release, and distribution for specifics on manual configuration. Setting the gateway may not be necessary.
You should have a wired connection from your computer (laptop) to the LAN side of the TP-LINK W8980. Try another OS or OS distribution on another computer as well if you're still not able to connect.
If that doesn't work, I would reset the TP-LINK W8980 and access as you did originally and try enabling the unit's DHCP server (or keeping it enabled) on the LAN side. The unit should be a DHCP client on the WAN side. And make sure you don't have the TP-LINK W8980 in bridge mode. Unless your intent is bridged mode. But it sounds like you may want your own private LAN.