[HELP] Unable to flash firmware on Xperia SP C5303 using flashtool

So, the problem is that Xperia SP was working nice on Carbon 4.4.4 but then I flashed a kernel with bad WiFi module. That had a builtin TWRP (I previously had CWM and backed up everything using CWM)... then I did a really bad thing. I renamed boot.img from CWM backup to boot.emmc.win (TWRP compatible) which subsequently flashed CWM and old kernel. I forgot to restore my SYSTEM as some kernel parts are there (I knew it wouldn't work but I had plan to restore it via CWM)

Then I rebooted into recovery but it didn't reboot. Instead it showed me Sony logo and red LED. Then black screen and repeats same. I learnt how to hard reboot and it did no good. I have unlocked bootloader and I'm trying the flashtool but it won't recognize my phone (I have installed C:\Flashtool\drivers\*) on Windows 10 but it didn't do any good either.. Now when I reboot into fastboot mode it shows me blue LED but isn't detected by flashtool;
Same is with the Flash Mode. Green LED but no connection. On the notifs panel on PC It shows that device not recognized. On Device manager it shows: Unknown USB device (Device descriptor request failed)

I wanna install the drivers but they're already done. I reinstalled them twice just for surety's sake... Any suggestions to install drivers and flash the firmware? I don't know much about Sony as this is not mine, this is a free device that no one uses in my family. I own jfltexx