Hub won't reconnect after powering off

Having had slow connections and regular drop-offs, 2 weeks ago, I followed VM instructions to reboot my Hub 4 by powering it off, leaving for 30 secs, checking all connections, then powering back on. On power up it went through the usual boot cycle, but after multiple cycles, still wouldn't connect. This was in the morning. I left it powered on and it continued the boot cycle all through the day with no success. By the following morning, it had managed to reconnect itself and all was well. Then yesterday, I accidentally turned the power off to the hub and have subsequently been unable to get it to reconnect. It is stuck in a permanent loop of boot cycles. I have tried powering off and on a couple of times, but then just left it powered on overnight in the hope it would eventually reconnect as before, but no luck. It cycles between flashing white light, solid white light, flashing blue light, flashing white and blue light together, then no light. I have checked all connections, disconnected any non-essential LAN cables, but nothing seems to work. Can anyone offer any advice please?