I bought an Archer D50, it worked properly in the first few months, but then I found that the internet is intermittent. The router shows orange at that time, and I found this error message on the basic page once I logged into the router-- Please configure your DNS server manually. 

I tried to power cycle/reboot/reset but no avail, I also changed the DNS server manually to 8.8.8.8/8.8.4.4 as the error message. Nothing changed.