If you can use the same cable and ethernet port to connect to the router with a laptop, or other computers, then you have isolated the problem to your non-connecting computer. Plug in the computer with the connection issue with the same ethernet cable. Next, open up command prompt
and type in the command "ping 127.0.0.1". This command checks your NIC card to see if it is working properly (if you get "Reply from 127.0.0.1", then your NIC card
is good, but if not, then you need to replace your NIC card.). If your NIC card is good, ping your default gateway (i.e. using a linksys with a default IP, type "ping 192.168.1.1" in command prompt) Your router's private IP Address, which can be found by successfully connecting another pc and, on the connected pc, typing "ipconfig" in command prompt, is also known as the default gateway. If you get 4 "Request timed out.", or "Reply from 169.X.X.X" ("X" being any number), then your network connection settings on your pc are incorrect. To fix these settings, assuming that you have DHCP
enabled on both your router and the computer being troubleshooted, use the commands "ipconfig /release" and then "ipconfig /renew" in command prompt. Give the computer a minute or two to allow the computer time to acquire a new IP Address, and the correct configuration from your router. Now your computer should be connecting properly.