D-Link DIR-300 Router not working properly

I have a DIR-300 Wireless router that has been working fine until recently. A few days ago the internet connection suddenly went off for all the computers in the house (both wired and wireless), however, the router page stated that internet was online. I tried connecting my PC directly to the modem and yes, internet is still working. Also it seems the computer can't detect other computers on the workgroup while connected, so I figured it has to be a problem with the router.
Does anybody know what may be happening and how I can solve this?