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When you performed the factory reset, did the tablet go through the long process of reinstalling the operating system? After the process has completed, it should either restart or prompt you for a restart. If this did not occur, the process did not complete.
You need to have a full charge on the device before performing an update or a reset, and it should also be connected to the charger. Did you satisfy these conditions before each of these operations?
the device was fully charged and connected - I left it overnight to complete the update. In the morning it had the Samsung logo but did nothing else.
Okay. You did everything correctly, but, apparently, the process did not complete. You said that you did a factory reset, and that it showed that it had erased all data. But what happened next? It sounds like that process did not complete either.
I recommend that you repeat the factory reset and watch what happens at each step in the process.