mobile

In my Xperia Z, I am using Infected Builds Cyanogenmod 12.1 Lollipop rom

All things like Usb debugging, ADB, fast boot are working but that flash mode is not working......

when I press Vol down while connecting it turns Green but suddenly goes into red, I tried these things below

1) Using Flashtool
selecting flash mode then the ftf file and I waited for the notification to appear connect your phone
then I connected my phone pressing vol down again it turns into green but suddenly goes into Red

2) Using PC companion
I tried Repair Option, but that one also said me to connect my phone in flash mode
I also tried pressing vol up+ power button for a while to occur three vibrations (i.e complete shutdown) thn tried connecting to my pc while pressing vol down

3) Using Fast boot
I tried to flash Original boot.img but that too didnt work I dont know what else to do............

I am able to install new roms via recovery but I want install Original Stock Rom but Flashmode is not working If Anyone knows how to solve this prob please help me..............