Mac running Windows 7 unable to detect Mac hardware, Windows Support Software issue...how to fix (no USB)
The answer, you referred to in your question, started out as an answer to the question Boot camp install of Windows 7 issue, no bootable devices. This question was often asked by owners of older Macs where the optical (DVD) drive was either damaged or replaced by a second internal HDD or SSD. The improved answer, which you referred to, was thought to be general enough to cover later Macs with no internal optical drive, but could still support a BIOS booting Window 7. However, this answer has proven to fail at step 10 for several model Macs where neither a keyboard, mouse, or trackpad would work. Fortunately, other questions/answers have been posted (such as Is it possible to use Boot Camp with Windows 10 from an external HDD?) where this fatal step 10 can be avoided. Since your updated question indicates you can get a keyboard, mouse or trackpad to work with Windows 8.1, I posted the instructions below for installing Windows 7.

Instructions for Installing Windows 7 SP1 using Windows 8.1 ISO


  This method does not use VirtualBox. Instead, the method relies on being able to boot from a Windows 8.1 flash drive. However, if this does not work out, a virtual machine could be use, but the instruction for doing so have be omitted from this answer.


The following files were downloaded from the internet. You can substitute files from another source, if you wish.


Windows 7 Professional SP1 English (64-bit) from this Microsoft website: 
Download Windows 7 Disc Images (ISO Files).
Windows 8.1 English (64-bit) from this Microsoft website
Download Windows 8.1 Disc Image (ISO File).
The Boot Camp Support Software 5.1.5640 from this Apple website.


The drive letters are given below along with a described. If you get different drive letters, then make the appropriate substitutions.


Drive C: is the fourth partition on the internal drive. Here I assume this partition has been MS-DOS (FAT) formatted and named BOOTCAMP by the Yosemite Disk Utility application
Drive D: is the bootable Windows 8.1 flash drive. Basically, a flash drive created using the Boot Camp Assistant and the Windows 8.1 ISO.
Drive E: is a MS-DOS (FAT) formatted flash drive containing the Windows 7 SP1  files.
Drive F: is a MS-DOS (FAT) formatted flash drive containing the Boot Camp Support Software files.



  Note: Here, I assume different flash drives were used for Window 7 SP1 and the Boot Camp Support Software, although an individual flash drive could be substituted.


Use the Startup Manager to boot from the Windows 8.1 flash drive. You should see the following image.



Press the shift+F10 key combination to open a Command Prompt windows, as shown below.



Enter the commands shown in the example below.

Microsoft Windows [Version 6.3.9600]


X:\Sources&gt;wmic logicaldisk get volumename,name
Name  VolumeName
C:    BOOTCAMP
D:    WINDOWS8
E:    WINDOWS7
F:    BOOTCAMP5
X:    Boot


X:\Sources&gt;format c: /fs:ntfs /v:BOOTCAMP /q
The type of the file system is FAT32.
The new file system is NTFS.
Enter current volume label for drive C: BOOTCAMP

WARNING, ALL DATA ON NON-REMOVABLE DISK
DRIVE C: WILL BE LOST!
Proceed with Format (Y/N)? y
QuickFormatting 204.3 GB
Creating file system structures.
Format complete.
     204.3 GB total disk space.
     204.3 GB are available.

X:\Sources&gt;dism /get-imageinfo /imagefile:e:\sources\install.wim

Deployment Image Servicing and Management tool
Version: 6.3.9600.17483

Details for image : e:\sources\install.wim

Index : 1
Name : Windows 7 HOMEBASIC
Description : Windows 7 HOMEBASIC
Size : 11,710,161,360 bytes

Index : 2
Name : Windows 7 HOMEPREMIUM
Description : Windows 7 HOMEPREMIUM
Size : 12,222,587,449 bytes

Index : 3
Name : Windows 7 PROFESSIONAL
Description : Windows 7 PROFESSIONAL
Size : 12,122,886,417 bytes

Index : 4
Name : Windows 7 ULTIMATE
Description : Windows 7 ULTIMATE
Size : 12,285,492,779 bytes

The operation completed successfully.

X:\Sources&gt;dism /apply-image /imagefile:e:\sources\install.wim /index:4 /applydir:c:\ /checkintegrity

Deployment Image Servicing and Management tool
Version: 6.3.9600.17483

Applying image
[==========================100.0%==========================]
The operation completed successfully.

X:\Sources&gt;dism /image:c:\ /add-driver /driver:f:\$WinPEDriver$ /Recurse /ForceUnsigned

Deployment Image Servicing and Management tool
Version: 6.3.9600.17483

Image Version: 6.1.7600.16385

Searching for driver packages to install...
There was a problem opening the INF file. f:\$WinPEDriver$\IntelHDGraphics64\autorun.inf Error: 0xE0000100.
Found 9 driver package(s) to install.
Installing 1 of 9 - f:\$WinPEDriver$\AppleBluetoothBroadcom64\AppleBTBC64.inf: The driver package was successfully installed.
Installing 2 of 9 - f:\$WinPEDriver$\IntelHDGraphics64\DisplayAudio\IntcDAud.inf: The driver package was successfully installed.
Installing 3 of 9 - f:\$WinPEDriver$\IntelHDGraphics64\Graphics\igdlh64.inf: The driver package was successfully installed.
Installing 4 of 9 - f:\$WinPEDriver$\IntelxHCISetup\Drivers\HCSwitch\Win7\x64\iusb3hcs.inf: The driver package was successfully installed.
Installing 5 of 9 - f:\$WinPEDriver$\IntelxHCISetup\Drivers\HCSwitch\Win7\x86\iusb3hcs.inf: The driver package was successfully installed.
Installing 6 of 9 - f:\$WinPEDriver$\IntelxHCISetup\Drivers\xHCI\Win7\x64\iusb3hub.inf: The driver package was successfully installed.
Installing 7 of 9 - f:\$WinPEDriver$\IntelxHCISetup\Drivers\xHCI\Win7\x64\iusb3xhc.inf: The driver package was successfully installed.
Installing 8 of 9 - f:\$WinPEDriver$\IntelxHCISetup\Drivers\xHCI\Win7\x86\iusb3hub.inf: The driver package was successfully installed.
Installing 9 of 9 - f:\$WinPEDriver$\IntelxHCISetup\Drivers\xHCI\Win7\x86\iusb3xhc.inf: The driver package was successfully installed.
The operation completed successfully.

X:\Sources&gt;bcdboot c:\windows /l en-us /s c: /f bios
Boot files successfully created.

X:\Sources&gt;diskpart

Microsoft DiskPart version 6.3.9600

Copyright (C) 1999-2013 Microsoft Corporation.
On computer: MININT-DQVBS9Q

DISKPART&gt; select volume c

Volume 6 is the selected volume.

DISKPART&gt; active

DiskPart marked the current partition as active.

DISKPART&gt; exit

Leaving DiskPart...

X:\Sources&gt;exit


After the Command Prompt window closes, click on the red X. When the popup shown below appears, click on the Yes button.



When the Mac restarts, hold down the option key until the Mac boots to the Startup Manager. Next, hold down the control key while selecting Windows on the internal drive.

After Windows 7 finishes installing, you will need to run the Boot Camp Support Software installer.

Suggestions, If You Can Only Get a Keyboard, Mouse or Trackpad to Work.

If only an external or internal keyboard works, you should still be able to navigate by using the keyboard. Once you have installed Windows 7 and run the setup utility included in the Boot Camp Support Software, the keyboard, mouse and/or trackpad should work.

If you can not get the keyboard to work, but can get a mouse or trackpad to work, then you can use the on-screen keyboard. When booting Windows 7, you will see the image shown below.



If you click on the icon in the lower left, you will get the following popup. Select Type without the keyboard (On-Screen Keyboard), then click on the OK button.



The result should be the appearance of the on-screen keyboard, as shown below.