The easiest and fastest diagnostics you can run is to swap for a known good router. Hardware does fail over time.
My two year old Efficient Network router will no longer connect to the internet.
I cannot ping the router and it will not connect to the internet. The Test light blinks every second, per the manufacturer's guide notes, but the other lights do not flash as they used to and it is clearly not getting the IP address. The router does get quite hot when in use and I have been in the habit of leaving it switched on all the time - should I switch off when the PC is off?
I don't really think the router is dead I think the firmware has become corrupted by ZoneAlarm which I have removed and I have subsequently reformatted the hard disk and reloaded Windows 98SE. The Efficient Network website has 'kernels' for download which I assume are for used to load the firmware in the router? However, if I can't ping/connect I don't see how I can check the settings.