I was working happily with my WL-520g for a couple of years.
One day it stopped working the following way:
When I connect two computers to the router - 2 LAN or 1WAN + 1LAN - after few minutes the router goes "mad" - all 4 LAN leds begin flashing, and the computer reports "network cable is unplugged". Each "flash" it connects and disconnects the network.
I can connect the router to the WAN modem or not - the behaviour is the same.
Latest firmware 1.9.5.6 does not change the situation.
Tried to reset by reset button - no change.
In spite it's out of WL-500g topic - may be you have some common procedures / ideas / links etc.
Thanks a lot
Mike