Failed to unlock the bootloader for Xperia SP

Hi, I'm trying to install my flashboot drivers. But everytime i do that, they dissapear from folder. I tried different versions of flashtool drivers ( 0.9, 1.3, 1.5 ) Always same result. I disable driver signature verification but it didnt work. Tried to replace some USB files in windows 32 / drivers but it only created another issue. I know there are couples post how to fix it for windows 8 but I'm using windows 7 but nothing seems to work. I'm out of idea. I followed this guide http://forum.xda-developers.com/show....php?t=2354721 but my windows wont start driver installation because for some reason they wont stay in my computer.
Trying to unlock Bootloader for Sony Xperia SP C5303