Garmin stuck on diagnostics

My Garmin 1030 has been sitting around for several months unused. When I turned it on, it boots to some sort of diagnosis screen as shown in the attached image. 

Whilst in standby and with the battery at near-zero it appears to have updated itself to a firmware version (9.10) which isn't listed on the garmin download page (https://www8.garmin.com/support/download_details.jsp?id=12819) and it won't sync with Garmin Connect so I'm unable to flash a different firmware. I also cannot do a reset by holding the power button for 10sec - it reboots as soon as I hit power off and comes back to this screen (sometimes it shows a bunch of coloured rectangles).

Any ideas how I can recover?