What Hardware version is your router? Look at sticker under router.
What
Firmware version is currently loaded? Found on routers web page under status.
What region are you located?
Try single mode G or N or mixed G and N?
Channel Width set for Auto 20/40Mhz or try 20Mhz only.
Try setting a manual channel to a open or unused channel.
What security mode are you using? Preferred security is WPA-Personal. WPA2/AES Only. AES has the best performance.
Any other WiFi routers in the area? Use
InSSIDer to find out.