From the sounds of it, there's likely a setting in the apartment building's WiFi network that the Roku doesn't like. Your Express only supports 2.4 GHz, and with some access points the Roku will not correctly connect to an access point that has the Mode set to G/N. Normally it's only been reported by people that use a cable company for their Internet, and it's possible that's what your apartment complex is using. In these cases, changing the Mode setting to B/G/N has resolved the connectivity problems.
I also just noticed you are saying it doesn't see any networks available. On 2.4 GHz, Roku supports channels 1-11. Some access points will self-assign channel 12, 13 or 14, and if that happens your Roku won't even see it. In North America those channels shouldn't be used anyway, but it still happens. Since they suddenly disappeared from view, a channel change to one of those unsupported channels seems likely. But I would still expect you to see some sort of connection, even if it's not the apartment's. When I scan from my home, I can see more than a dozen of my neighbor's access points, even though I can't connect since I don't know their passcode. 🙂
If your cell phone offers an Internet hotspot, see if your Roku will detect it. The phone hotspot will be turned off by default, so you'd have to enable it to test that. If your phone doesn't have one, perhaps a friend would let you test with theirs. If your Roku can't see even the phone hotspot, then my guess would be a hardware failure of the Roku. It's an electronic device, and sometimes they simply fail without warning. Roku only has the Express on sale right now, and I'm not a fan of that model. For a little more money I much prefer the Express 4K+. Dual band WiFi, WiFi Direct remote, and much more powerful than your older Express+ 3910.
Dan
Roku Community Streaming Expert
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