I can't use flashtool due to this problem
Manufacturer : SONY
Model : C6603
Bootloader : UNLOCKED
I press volume down as I connect it to PC the led blinks red then green then turn off but my PC can't detect it so I disconnect it from PC and I try to turn on the phone it didn't turn on so I made a hard reset and it turned on. So I recognized that my phone was stuck in flashmode.