Before you go the hard reset route, here is another option.
On the computer you have attempted to access the router from, check out your current wireless configuration. Right click on the wireless icon in the notification tray, and choose "Status". Click the "Support" tab, and check if your computer is getting an IP from the DHCP server (if you have dynamic ip). If it looks like you aren't, click the "Repair" button, and let it go through the repair process, about 30 seconds. If it comes up with a new IP for your computer, re attempt to access the router. Go through all of your settings, and see if anything is different, particularly the DHCP settings. If you haven't done it yet, be sure to set a non standard password for your router, and run some sort of encryption. Turn off SSID broadcast, and secure your network!