Stuck in "Connecting to the ReadyNAS Admin Page" after upgrade to 6.10.5

Hi,

I've had my ReadyNAS for a little over six years and this is the first time I've had an issue with it that can't seem to be simply resolved.  I've searched online and there's a similar description of the issue here but it was a while ago and seemed to be linked to a different firmware upgrade. 

https://community.netgear.com/t5/Using-your-ReadyNAS-in-Business/Stuck-in-quot-Connecting-to-the-ReadyNAS-Admin-Page-quot-after/td-p/1534391 

In summary, I updated the firmware to 6.10.5 about two weeks or so ago and had no issues at the time.  Yesterday I went to get into the admin page but it's stuck in an endless loop of asking for the password, loading the admin page and then, just as the admin page loads, it flips back to the start and asks for the password again.

I've looked at the instructions on the other thread and this is what I've tried/not tried so far:

1. I've Cleared the browser cache, tried a different browser and also logged on from another PC with no changes. 

2. My box is connected to the router (and hence the net) but I've never connected to it via the internet.  I've rebooted it twice with no changes.  (NB: I normally have to say "yes" to firmaware updates.)

3. I haven't tried taking the disks out and seeing it it will boot to safe mode as that seems drastic at this stage. 

4. I can't see how to download logs as the instructions indicate that I have to get into the admin page first.

I'd appreciate any pointers I could get please?