You could try going in to Sys pref>networks>airport>advanced. Remove all preferred networks. Then go back to the airport main screen. Turn off your airport and then reboot. While rebooting, reset your modem and router again. Make sure you unplug the power bricks from the wall outlet and the router and modem from the power cord. Leave for at least 30 seconds. Now plug everything back in. When OS X comes back up, go back to the airport properties and turn the airport back on. Also, add your network back to the preferred networks list in the advanced options menu.
If that doesn't help. Repeat all the steps, except when you have your modem and router unplugged, completly reset both by holding down the reset button on the backs of each unit, for at least 30 seconds. Then continue on. You will need to setup your router again by loging in to it at 192.168.1.1 and configuring your security settings. Netgear admin signin is usually, name: admin, password: password.
If that doesn't work you can try upgrading the firmware on your router.