A user reports that their computer is not connecting to the Internet. After checking that the computer has a valid IP address, you suspect the issue could be with the computer's network card. You replace the network card, but the computer still can't connect to the Internet. What should you do next?
Inform the user they need a new computer.
Replace the network card again with a different brand.
Establish a new theory, such as checking the network cable or router, and test it.
Assume that the Internet service is down and wait for it to come back on its own.