Sounds like a fault in the DC power side of the router to me.
My own WGR614 died only the other day after 3 years of loyal service.
It kept disconnecting me either wirelessly or via cable so I ditched it and got a new router.
I'd just go any buy a new one. They're pointless to repair unless you have a BGA machine and the skills to fault find the circuit.
And I'm not doing it for you.
You can pick up a wireless router for about £45 now and if you are using it plugged into the ethernet socket of your modem you don't even need to bother setting it up or installing drivers.
Just plug it into your modem and power it up. Log in and then change the default password into the settings and that's it.
You're good to go.