Can't get into Flashmode or Fastboot, Can get into recovery
So I bought this Xperia SP off a friend, It had the ExistenZ 3.0.0 Rom and I updated it to the 3.3.0 OTA version. Obviously this means I can get into both recoveries that come with the ROM TWRP and Philz. I want to go back to stock now but I can't flash the stock .tft with flashtool or SUS because I can't get into Fastboot or Flashmode. When I plug the cable in and hold Vol + to get into Fastboot it does nothing and just boots normal. When I hold Vol - the main green led comes on like it should, I get an error on the PC saying the device cannot be recognised and it has malfunctioned before it could be connected and then the Green LED goes off after around 5 seconds and then it restarts and continues to boot normally. However once the main boot sequence has started I can get into the recoveries using the Vol +/- and I can flash ROM's. Is this a kernel issue ? Also I think there maybe a loss of baseband because I keep getting that no sim can be recognised but I'm unsure which is why I want to go back to stock. I also can't see if my bootloader is locked or not because the service menu app crashes when I try to see :/ It never actually gets into fastboot or flashmode.
What I'm asking is, How and if I should try and flash the stock kernel to see if I can get the FastBoot and FlashMode back.
I have Windows 8 and have installed the correct drivers by disabling signature enforcement.
Edit: I can see that it is actually trying to get into flashmode
Thanks in advance guys
[Nokia Lumia 800 - Black] Mango 7.5
[HTC One X - White] Android Revolution HD
[Samsung Smart Pc Pro XE700T1C] Dual booting Android and Windows 8.1
[Sony Xperia SP] Existenz 3.3.0 - currently malfunctioning
Used to be a hardcore gamer, Now just a casual teenage tech nut.