Originally Posted by Larry2999
Sounds like a stuck power button then. Thankfully, this can be routinely fixed at a tech shop or by yourself if you have the right tools and skills for this. Sometimes it doesn't even require replacement of the power button which can be bought cheaply on places like that online auction site.
Can confirm that it's a stuck power button; tapping it continuously with an end of a chapstick tube while the phone booted got us all the way into Cyanogenmod; we confirmed that TWRP flashed successfully as well. However, we as soon as we stop tapping it, it goes back to the previous behavior.
We're now looking for some guides online to fix it, seems mechanical if tapping it continuously will keep it unstuck for short amount of time.
Thanks again guys