We have a Linksys Cisco router that also has wireless capability on it, it is working perfectly fine before for the wireless connection, but when we stopped using it for more than a month since we just connected the computer to the modem directly, it stopped working now. We already pushed the small reset button on its side, but still nothing happened.

Greyfox, August 2011

The router probably have the option of disabling wireless communication. Maybe you disabled wireless broadcasting when you started using cabled connection. A small thing that is very easy to forget after just a few days...
Open the configuration page of the router and re-enable wireless connectivity.

It's also possible that during the last month one of your neibors started using his own wireless home network and it conflicts with yours. Try switching to another channel.

Electro, August 2011