unfortunately it was quite serious haha - i've dissasembled it with quite difficulty, it feels like HP notebooks designs were meant to be puzzles 
but i tried cleaning everything - and there was a lot of broken plastic and dirt inside of it (maybe that was what wrecked the mobo). I also wasted some thermal paste on it, hoping it would work after the cleaning, and that i wouldn't have to open that ever again - but it changed nothing, the notebook still turns on, but won't even start the bios.
at least i was able to harvest some cool components: 2 DDR3L RAM sticks, the Ralink wi-fi/bluetooth module, a 300gb HDD, the screen and a DVD drive
Anyways, thank you for your help! I guess this thread could be closed.