Why won't my Android ADB install?

[Dave20144]

I want to unlock my bootloader but Android ADB won't instal

Hi there
I want to unlock bootloader on my xperia mini pro but when I want to instal the usb drives the installation stops and it says that the Android ADB interface won't instal cuz its broken/missing. The driver just won't instal

I don't know what to do at this point. Please help
The usb debugging is on and yep I connect the device properly.