[AC Question]

My Galaxy S5 (SM-G900F) suddenly got stuck in a bootloop yesterday. It wouldn't get past the Galaxy S5 screen 9/10 times, or it would get through and stay at the Samsung screen. After trying the go-to solutions, like clearing my cache/rebooting etc, I decided to just take my loss, wipe the phone and install clean firmware (I used the ODIN method and installed the latest version of the firmware). Everything went according to plan and the phone started fine. After happily configuring the phone again, I briefly switched the display off. After that, it wouldn't turn back on: the buttons would flash and i could hear the screenshot sound, but not always either. The only way I could turn the phone off was by taking out the battery. Now I'm stuck in the bootloops again: either the phone does the exact same thing as before, or it shows nothing except for the blue notification LED. Sometimes (again, this randomly happens once in about 20 tries) it turns back on through recovery mode, only to become unresponsive again once the display goes off.

Now my question is: is this a software related problem? If so, I think I might just let my go-to phone repair store do a clean install for me. Or could it have something to do with hardware? Maybe battery or a loose cable somewhere?
I apologise if the text above is confusing, English isn't my native language and the problem is just very weird in general.