Sorry to hear you're having driver troubles. It's hard to tell exactly what the problem is from your description, but I'll give you some steps to try and fix the problem quickly. After that I'll explain the full situation a bit so you can help decipher what you're seeing:
To (hopefully) fix the problem quickly:
* Open Device Manager window.
* With the LeoStick plugged in, press the Reset button.
* The LeoStick bootloader should start. If the driver is installed OK, you'll see the bootloader pop up as a COM Port. Otherwise, you'll hopefully see it pop up as "Unknown Device".
* If the bootloader shows up as a COM port
, fire up the Arduino IDE with an example sketch like Blink loaded, and the Board Type set to "Freetronics LeoStick" (either V1 or V2, the Getting Started Guide explains these steps to have this option and know which LeoStick type you have
.) Then press Upload and then shortly after that press the Reset button again to trigger the bootloader. It may take a couple of tries to get the timing right, but after the first upload everything should go back to normal and you'll be able to upload without any manual intervention.
* If the bootloader doesn't show up as a COM port
, wait and see what happens a few seconds later when the bootloader ends and the sketch starts running. You should see the Unknown Device go away and another device appear. What shows up then? The next step will depend on what happens after that.
Here's a longer explanation:
LeoSticks (also Leonardos, but I'll focus on LeoSticks to start with.) appear as two different USB devices - the LeoStick Bootloader and the LeoStick Running Sketch. The bootloader is baked into the LeoStick before you get it, the running sketch is what you upload from inside the Arduino IDE. The bootloader device appears when the LeoStick reset button is pressed, then after a few seconds if no sketch is uploaded it will disconnect automatically and the "LeoStick Running Sketch" USB device should connect. On Windows, each of these should come up as a different COM port but the COM ports should appear separately not both at once.
The USB IDs can vary depending on your LeoStick. The bootloader could be VID 20A0 PID 4151 ("V1 bootloader"), or it could be VID 26BA PID 0002 ("V2 bootloader"). The running sketch should be VID 26BA PID 0003.
The bootloader should always appear successfully as a USB device. The running sketch might fail to appear if it's been somehow flashed with a wrong program or something has gotten corrupt.
The Leonardo, as opposed to the LeoStick, has a different set of USB IDs for bootloader and sketch. These should never be ever seen on a the LeoStick (and similarly the Leonardo drivers should not be needed for the LeoStick.) The only exception will be if you accidentally uploaded a sketch to the LeoStick with the Board Type in the IDE set to Leonardo. This is not really a problem, in fact it works, it just means you need both drivers installed - you should see "LeoStick Bootloader" come up first, then a few seconds later "Leonardo" connect as the sketch runs.
One other note is that "failed to start" errors in Windows may imply a lower level problem with the USB connection or USB port. Perhaps try a different USB port, especially if you're using USB 3.0 ports try a USB 2.0 port (I haven't had any problems with USB 3.0 ports myself, but some USB 3.0 controllers can be fussy.)
Please let us know how you get on.