[Q] Alps N9500 wont boot; neither bootloader, charging screen nor recovery works; topic

Dear Community,

as an amateur in the Android scene, I call for help.
This is an act of sheer desperation since I try to fix my phone (Alps N9500 MTK6589) for about 6 hours now..
A few months ago, I rooted my device via MTK Droid Root & Tools v2.5.3.
After a system crash of Android (4.2.1), my device is not able to boot up.

Symptoms: -The only reaction I get is a black screen. (backlights are on, but no screen content)

What i tried:
1. Neither the bootloader nor recovery mode will come up. .
2. Connection via adb worked fine
3. Tried to flash my device with the stock ROM -> Bootloop -> adb wont work at this state

Furthermore, I did a MemoryTest with SP Flash Tool v5.1352.01:
External RAM:
Type = DRAM
Size = 0x40000000 (1024MB/8192Mb)
NAND Flash:
ERROR: NAND Flash was not detected!
Could this be the problem?
(Unfortunately, I think the bootloop is something I messed up..)
I would be glad to see a solution for my problem and am very thankful for every contribution leading to the solution.

Sincerely,

An Android-Noob