@EEEEEES well, arp -a will mostly likely be looking at the arp cache, not a live report. There’s no reason to maintain it live. Ping the unit, then try an arp -a afterwards. (or ping the entire network with a tool or try pinging your subnet’s broadcast IP (192.168.x.255 most likely).
Got an old router kicking around? Borrow one from a pal? Just set it up in default mode, hard reset the 57925 and see if you can connect. If you can’t it’s pretty likely it’s defective, I’d think. If it does….then it’s your existing setup. Debugging … change only ONE item at a time. Give it a shot and let us know what happens.