Medion - P61468 (MD44468) - diy help

Hello everyone,
First, Im sorry if I didnt choose correct place/options to start this topic.
So I rly need help, and I dont know who else to ask. I have almost new bluetooth speaker - medion P61468 (MD44468) - used maybe 5 times and it died. It shows that it charge and it shows when battery is full (red and green led) but I have no display and I cant use any function to play sound. So I try searching for parts, mainboard, I look for broken speakers as well, I cant find anything. So I unscrew it check power supply and battery and its good, I check power swich, also good. So I guess main board is causing issue.
So you probably wonder what help do I need, any tip on what to look on mainboard, what to test and try replacing it would be helpful.

OR tips with this:

I have speakers, power supply and almost new battery, I was thinking why not use it for parts and build my own speaker, I know its possible just Im not rly good with choosing parts because lots of things I dont understand (compatibility things).
So I have 2 x 3ohm-40w speakers, and 2 x small one (I know name of those on my own language but on english idk how you call those), so I need some bt audio controller for those and Im not sure do I need battery controller or it has one inside separated from main board ( they glue it so much that I gave up from looking inside battery case for now). Im also not sure can I use power supply from the speaker (12v).If anyone have some tips, guides, videos that I can watch that would be helpful or links with parts that I need and that are compatible with these speakers and voltage that I have... that would also be great
So please guide me if you know what can I do with this medion garbage that I have and dont buy medion speakers, I still have warrenty but its cheaper for me to buy new one than drive to store where I bought this and dont trust their pictures, they have 2 cosmetic speakers made of plastic with 0 wires inside.