So, I bought my SDG805, also from Futu Tech GmbH, back in 2014 and used it a bit in the beginning. Have then had a couple of years where my electronics workbench has been mostly collecting dust. Tried using it a couple of weeks ago and got stuck on the boot screen.
I guess I'm screwed. It is definitely more than three years old.
Contact Siglent.
There is solution.
Do you have installed FW version what support recovery using USB flash. (I guess not if I think your timeline)
If you have this, then it is perhaps more easy. (if your SDG failure is this known type)
If not, there is still solution (including some nice bonus) but it need open SDG and hardware activate recovery mode and then run recovery what need special file from Siglent and after recovery then remove this hardware activation.
It have many times told that it is very important update to FW version what support USB recovery.
And also now, if anyone still have SDG800 model with OLD FW then URGENTLY update it to version what supprt USB recovery. Not only support USB recovery but also more new FW do not go to thiss situation so easy at all afaik.