Default [HELP] entering flashmode on xperia sp

I want to root my Xperia SP firmware version 12.0.A.2.254
I'm following Divaksh's method:
How do i enter flashmode? I tried holding vol down and then connecting the usb cable but nothing happens! I get the "USB device not recognized" msg on my comp (win8 x64)..
And on my mob, a green light appears and then that charging logo comes up!
Do i need to download any ADB drivers? If yes PLEASE send the download links! I tried ADB driver installer but It doesn't seem to support x64 OS