Xperia X Installation Fastboot Driver (Windows 8)

Hi guys! Trying to install sailfish x on WIn 8. In device manager, there is no 'S1Boot Fastboot'-Device. 2.4 Find the ‘S1Boot Fastboot’ device in the tree. If it is not correctly installed, it will show a warning sign. There is no warning Sign. Trying to add a Legacy Driver with the downloaded Driver doesn't work. The driver installs, but it says, that the installed drivers may not work properly. Skipping this step trying to fastboot with the given code says "Waiting for any device". I am really desperate. Please help! Thx!