Help Star N9189 (MTK6589)

Hi everyone !
I’ve been looking now since 5 days for a solution..
Here’s the thing :
I was changing the bootloader of my N9189 and when I rebooted the phone, I only got a black screen (I could answer calls, do stuff, but couldn’t see anything with that black screen)
I tried to reset it from turn_on+volume_down and volume_up but that didn’t solved the issue
Then, I tryed to reflash it (my phone was already rooted but had the official rom, (I never changed it)) and I got with sp flash tool the 4032 error..
I followed many tutorials for mtk devices and I also found a solution to pass the 4032 error (all I had to do was to install a S5 mtk rom first and then, I could try to install the rom I want to install to use back my phone)
Well, done. (to be precise : when I turned on my phone, I had a white screen but then nothing, phone turns automaticaly off)
Then I could install the only N9189 rom I found on needrom on my phone, all ok, install and upgarde completed succesfully
But when I try to start the phone, nothing happens !
Just to try, I installed a Z908 rom version and that made a white screen boot loop this time.. (I did the process with the S5 stuff to get rid of the 4032 error again to try that of course)
All this makes me think that it is just the rom I download which is bad, but I’m not really sure..

Could you guys please help me or have any ideas ?

Tanks in advance