Android won't turn on at all Basically the phone won't turn on at all, not normal boot, not recovery mode, not even the battery percentage show up while charging (just the battery icon with lightning, that's it). it stucks on one screen (battery icon/logo) and stucks there until it ran out of battery again.

But strangely, download mode is accessible, and when i tried to boot from that, the screen is stuck at the logo
my phone is Samsung Galaxy Tab S2 8.0 Inch

Help
It seems that you have bricked your phone. Download and unzip Odin on your computer. Then download the Stock firmware:
https://forum.xda-developers.com/tab-s2/help/tab-s2-stock-rom-t3199363
Then flash it using Odin. You can easily find a guide to flashing using Odin online.