1. are you sure you know how to get into fastboot mode? - turn the phone off, hold volume up and while holding it, plug the usb into your computer.
2. make sure you have drivers installed. Can be found in Flashtool/drivers folder. If you're not sure which ones to install, you can install all of them.
3. this is the guide how to unlock the BL.
http://forum.xda-developers.com/showthread.php?t=1363847
I'm sure you can get into fastboot mode, I think you're just doing something wrong maybe...Try installing the drivers first, then try to get into fastboot mode as I described. See if it helped.
P.S. the thanks button is there for a reason

:good: