Link>
Welcome!What Hardware version is your router? Look at sticker under router.
Link>What
Firmware version is currently loaded? Found on routers web page under status.
What region are you located?
Has a Factory Reset been performed?
What ISP Modem make and model do you have?
I recommend that you have the ISP check the phone lines to make sure they are in good working condition and filtered correctly and the DSL modem is getting good signal.
Any cordless house phones?
Any other WiFi routers in the area? Link> Use
InSSIDer to find out. How many?