Lose Signal Even With Router Plugged In Directly?

For over a year there was no issue with the wireless router, then all of a sudden the connection was lost even though the signal was strong. When trying to figure out what was wrong, I accidentally reset the router. I had not used one before, so I am not too knowledgeable. The router had been my previous roommate's, who had set up the password, etc and I had been using it with that set-up, but now I had no password. I tried to reconfigure and set up a new password through the D-Link administrator, but could not get it to work. It is a D-Link DIR-655 and I am using an iMac. I finally just bought an Ethernet cable and plugged in directly,since I had no password protection. But even with the cable plugged in, I will lose the connection and have to restart the router to get it back - which has even happened while I am using the internet.