You may be experiencing either an attack by alien entities, or some electrical interference from other household appliances, or even networks close by. If possible, try and see if you can switch what channel your wireless runs on. I know I can do that through my ISP.
+1 to switching channels. Also, see if there's a firmware upgrade from the router's manufacturer. I had problems on one of my client's Linksys/Cisco routers until I upgraded it to the latest firmware.