smlunatik is correct. You are going to have reconfigure all the setting again. If you all else fails, ask someone who knows how to configure routers in your area. In the future, why don't you guys backup your settings on you local machine.
Tools ~>System
Save the config file to your hard drive. I'm sure Macs have it similar.
If you can't login, get a paper clip and do a hard reset by holding down the reset for at least a few seconds until all the blinking light turn off and then reboots itself. The router should reset to factory settings just like smlunatik said.