Hey mate, sorry to hear your light stopped working, that's shit! At least you had a backup ready and waiting. Smart move, always a good call. I have a smaller SF1000 that's a backup (used) if ever my big SF4000 breaks. Will keep me going until I can get it sorted, like how you are here for example.
So, with the light. I don't have an answer specifically for you to get the light fixed and I very much doubt anyone else would have a definitive answer for you honestly barring the manufacturer.
The best and only advice I would be happy to give you is simply this. Return the light. Don't go wasting your time and energy trying to fix it or finding out why. Just simply return it. Be thankful it happened now and not 2 weeks after the warranty expires, which would have been expensive to say the least.
Your light and pretty much everything in the world is covered by a 30 day money back guarantee AND a 12 month manufacturing warranty, fact (at least within Europe).
Contact the manufacturer, send them pictures of the light and the bill of sale (the paperwork that would have been inside the box you got with the light) to save you from having to go back and forth, back and forth etc. I'm sure they'll honour their manufacturing claim without hassle and you'll be back up and running in no time at all.
Feel free to message here or send me a direct message on my page if you have any growing related questions.
Have a wonderful day and I hope you fix your problem soon mate =) =) =)