It must have been your PC's network interface which wasn't working temporarily for some reason. It may have just been a glitch, or a loose cable, or an intermittent hardware problem, even possibly a problem with your PC's memory. There are so many possibilities that it's very difficult to identify the actual cause. Check that your cables are all firmly inserted and cross your fingers that it doesn't happen again.
(Actually, on reflection, Broadstairs is right - it could have been a temporary loss of DNS.)