WiFi can drop out for many reasons which a lot of folk shared before at http://www.cnet.com/forums/discussions/samsung-smart-tv-suddenly-not-so-smart/
I've fixed too many of these. Most we move away from WiFi since it's subject to hard to diagnose failures, distance is half that of laptops and the list goes on. It's rare but usually a reset and distance reduction helps and yes, you write it's connected but if the distance is over 20 feet we get wired as a test.
Apps and Internet not connecting from my Samsung "smart" tv.
My tv has connected flawlessly for one year since purchase, so I know my set up is good. Nothing has changed.
My other wireless devices are connected to the Internet, so I know my network is good. In fact I am submitting this through my wireless network connected to the Internet.
I power cycled the modem and router plugged in the modem first and made sure it was connected, then powered up my wireless router.
Again, my wireless network is up, but my $2500 tv is not working.
Even worse, network status from the menu options says I am connected to the Internet!
Why are none of my apps or browser working?
No Youtube No Netlix very frustrating.
I see some of you had similar problem back in February. Any body having problem now and how did you fix it? Great many thanks if you can help me and others who may have similar problem, before I call waranty.

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