[HELP ASAP] Possibly soft-bricked phone, and flashmode won't work.

Hi there.

I'm using a Sony Xperia SP C5306. After attempting to install XperianZe OTA V3.0.5 (and Gapps), I find my phone stuck on the Sony Logo. It doesn't move. So, I do the sensible thing; I download a stock FTF (C5303_12.1.A.1.207_AU.ftf) and Flashtool, and attempt to install the stock ROM. But here's my problem; I can't get it to stay in Flashmode.

When plugging in my cable, I hold the VOL down button and the light goes green. Great! So the Flashtool starts flashing the FTF and my phone's green light goes out immediately. But it keeps flashing for a moment. And then the tool tells me suddenly that the phone has been disconnected. The phone goes to charge and sticks at the Sony logo again. This happens every single time.

TL;DR - My phone goes from flashmode straight to USB charge and I can't flash it to fix my softbrick.
If it's any help, my phone has a Locked Bootloader, and cannot be unlocked.

Phone not staying in flashmode (possibly just for a couple of seconds)

I managed to delete my system files (through TWRP). Thus I've been trying to flash my phone with the stock firmware (have been using the [Guide for NOOBS] for it), though after I connect the phone to enter flash mode (when flashtool asks for it) while holding the volume down button the green led turns on, flashtool doesn't says anything, and then the green led turns off, and then I see the Sony logo followed by TWRP.

I'm using the Xperia Flashing tool version 0.9.18.6 (by Androxyde), in the newer version I couldn't get it to 'see' the .ftf inside the app.
Quitting ADB nor using the 32bits instead of the 64bits version have helped.

Does anyone know a solution to this? :confused: