If you have done all that, and still it doesn't work, the only other thing left to try would be try it on a different WiFi. If it still doesn't work, then, if the device is under warranty still, contact the manufacturer about a repair or replacement.
If the device isn't under warranty any longer, then you would have to find someone who can repair it.
If it does work on the other WiFi, then your modem or router may be the problem.