Good morning, I hope I can help you.
First thing to check is the battery condition as it may have gone flat for some reason.
Try either jump leads with a donor car or a battery booster pack if you can get one.
I know you don't think it's a battery fault but it is where you must start. You have an electrical problem so you must check the power supply first.
Either jump leads or power pack will do. If the fault still exists when either are connected then we can go forward to do some other tests.