[sirmaru]

You folks may have reached the limit of your WiFi allotments on your router. I use the ATT Residential Gateway. It has a limit of 10 devices. Thus, every time a device is discarded, one must disconnect it from the WiFi net first. Otherwise, it's allotment is not reduced.

I had sent back a defective 3rd generation Kindle last year. First I had to unregister it from Amazon and then I had to manually disconnect it from the WiFi network (not just turn off WiFi). Had I failed to do so, my Residential Gateway would still be counting it towards the 10 limit.

If one fails to do this, one must reset the Residential Gateway altogether and start adding devices again.

Try disconnecting some unused WiFi devices like cell phones you no longer use. Then connect the Kindle 4 to the net. If you've discarded a lot of devices without disconnecting them from your net, then try resetting the router and add them back again one by one.

Finally, WiFi nets have range limits and could be blocked by physical obstructions. See if your problem occurs only in one place in your house.