@Nottoday So, could it be that your router is defective or something like that?
~ Jordan
@Michelle3 I don't think so because other devices (computers, tablet) are connecting just fine. As well as I've tried hotspot and even taken to a friend's house to connect and both rokus still refuse to do so
Pretty much gone through all the troubleshooting available to the end-user then. If any are less than a year old, then should qualify for warranty replacement. (https://support.roku.com/article/208757058)
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Would suggest trying to go one step up and purchase one of the newer dual-band devices (Roku Express 4k/4k+) so that you have the option of 5ghz. Not sure how you powered these other other Express units, but try powering either the replacement or your new one using the supplied power adapter at the wall rather than USB power port of your TV if you did that.
Sometimes an underpowered Roku device can lead to premature failure or won't power the device enough for the network chip to work properly . If you haven't already, try these Express units with wall power. (any 5volt 1amp cell phone USB charger will work).