BootCamp 5 - USB not working after drivers installed

Hello

I have a real problem to setup bootcamp for installing Windows 7 Pro on an iMac 21.5 (end 2012).

Normaly I would setup Windows with VMWare Fusion but this time we decide for a mac with the Apple BootCamp!

I erased my HDD and deployed it with an masterimage of 10.11.6. And tried to installed Windows 7 Pro with the BootCamp Assistant. Works till the boot camp drivers were installed. No USB devices are recognised

I tried the same with 10.13.2 and the result is the same!

So this is what I done

1) I own a Windows 7 Pro 64bit .iso file, the Product Key and an USB2 Stick.

I had problems installing the drivers using the Boot Camp Assist Tool. Then I decide to burn the .ISO file to an DVD.

2) I download the BootCamp 5.1.6521 drivers (the correct one for this iMac) and extract them to an USB2 Stick

3) I connect the USB Optical Drive with the Windows 7 DVD to the iMac

4) I start the Boot Camp Assistent and choose option (3) in the Bottem (Install Windows 7)

5) I split the HDD in 2 partition of each 500Gb

6) I set the Windows 7 Pro version and set the Language. The File are transferred to the bootcamp partition at the end I had to format the partition in the Windows Mask.

7) after a couple of reboots I was prompted to enter the Windows Product Key. Till that moment Apple USB Mouse & Keyboard are still working!!!

8) The next step was that the Boot Camp drives are installed automatically

9) after a restart I wasn't able to do anything! Mouse are not moving, Keyboard doesn't work

10) I reboot in OS X and connect an Apple Bluetooth Mouse. This works in OS X. The I reboot in Windows. Windows loaded the Bluetooth driver automaticly and the Apple Bluetooth Mouse was working.

11) Because I hat setup no Password, I was able to load all the 188 Windows Updates! But still USB ist not working.

The Problem is that the USB devices aren't recognised no at all. Not the USB2 Stick with the BootCamp5.1.6521-drivers, Not the Apple Keyboard, Not the Apple Mouse, Not the Apple USD Optical-Drive with the Windows 7 DVD

What can I do to get this work? I did this whole procedure twice! Once with 10.12.6 and later with 10.13.2

Please help me with some suggestion. I lost so many hours. It is really frustrated. I did the Bootcamp installation more as 5 years ago (I think it was 10.7 or 10.8) on about 15 pcs. iMac (with builtin optical) drives without any problem. Has the Bootcamp Assistent become so buggy?

I hope you are able to help me?