[Help] Xperia M probably bricked after installing TWRP into boot partition

Hi,
I was trying to install CM13 and GApps on my Xperia M when things started to go wrong. Finally I ended up trying to get TWRP running. Unfortunately I flashed the TWRP.img not only in my recovery, but also on my boot partition (or how do you call that).
The result is that my device won’t start up any more: when pushing the power button I only get one buzz and then nothing. I can push the power button a few seconds later again, with the same result. When I attach my device with a USB cable to my pc I get one red light flash, but I cannot put the phone in fastboot or flash mode (no green or blue led light). However, when the phone is attached, the flashtool indicates that the device is connected in flashmode. Unfortunately I can’t use flashtool to get anything installed (see log below). I should also add that the power up button doesn’t work anymore since long (so no way to get into fastboot anyhow) and that when charging the phone with a wall socket charger, I get a red flashing light (no constant red light).

I already tried everything I could find on this forum – especially the content of "[GUIDE] Recover 2012 and newer XPERIAs from SOFT-brick" was very interesting.
I mostly want to hear from you whether I can continue trying, or whether my phone is officially bricked!…

Thanks in any case,
tim