(Mac) How to make ISO file bootable on USB? (Repairing a Windows PC)

Testinny · 05 Mar 2021

Hello, TL;DR, I have an ISO installation file that I want to use to repair my Windows PC, but I can only access my Mac computer, right now. Is there a way to make my USB flash drive ready to repair Windows, with a Mac program?

After a series of blue screens, recently, my computer decided that it was tired of me rebooting in hopes that it stops crashing, so it is now stuck on the Windows Boot Manager, telling me that "The Windows Boot Configuration Data file is missing required information" and that I must repair it with the installation disc.
However, the disc that I have is 32 bit Home Premium, and I upgraded my system to 64 bit in 2018 with an ISO file that I downloaded legally on the Microsoft website with my product key, and I read that a 32 bit disc cannot be used to repair a 64 bit system. The file is named Win7_HomePrem_SP1_French_COEM_x64.iso, and its size is 3.25 Gb.
I still have that ISO file backed up online, but I have put the USB flash drive back to its original use of storing data, so I deleted every installation file on the USB drive.
I have seen guides on these forums mention "Vlite" and "Rufus," but I am not sure if Mac can run these. Is there a Mac program to make my USB flash drive bootable? Should I just drag and drop the files contained in the ISO file into the USB drive?

I thank you for your time.

SIW2 · 05 Mar 2021

Should I just drag and drop the files contained in the ISO file into the USB drive?

If the usb was formatted in windows as fat or exfat, you can probabaly just copy the iso contents onto it.

Or

Create Bootable USB Flash Drive on Mac OSX for Windows 10 (for clean install on PC) - YouTube

It is the same for win7

Bree · 05 Mar 2021

SIW2 is correct, you can just copy the files from the mounted ISO to the USB. If you need the USB to be bootable it should be formatted as Fat32, and if you want it to boot on a Legacy BIOS PC then you also need to mark the partition as Active.

Testinny · 05 Mar 2021

Thanks for the answers. I did what the YouTube video said and managed to copy the files that way, but when I boot, press F8 and select my USB drive and press Enter, it only shows a black screen with a flashing _ at the top left.
Next, I will try the other formatting option available on the Disk Utility "MS-DOS (FAT)" since exFAT did not work. I do not know yet how to mark a partition as active while unable to open my Windows session, is it what I did with F8? (I do not know much about formatting).
My PC is very old (2009) so I could see why the suggestions on recent guides would not work.

Update: After trying FAT, booting with the USB drive says "Non-System disk
Press any key to reboot" and I am still stuck.

SIW2 · 05 Mar 2021

My PC is very old (2009)

it only shows a black screen with a flashing _ at the top left.

It could be taking a while to load the wim into ram. Did you leave for about 2 minutes?

If there was nothing bootable, you would get a message.

Update: After trying FAT, booting with the USB drive says "Non-System disk
Press any key to reboot" and I am still stuck.

Too late now, you have reformatted it. It needs to be marked active ( in unix active is sometimes called boot ) . Is there some kind of diskmanagement facility on your mac a bit like gparted perhaps? I assume there must be. I have never had a mac, maybe somebody else can tell you where to look.

SIW2 · 05 Mar 2021

Quick glance on tinternet it seems terminal and fdisk is used for that. Surely there is gui for that kind of thing ?

Testinny · 05 Mar 2021

I know very little about the Mac computer, it is not mine, and the owner knows less than I do.
I guess I will try exFAT again, I only did let it run for a few minutes, I will try 10 or 30.

Bree · 05 Mar 2021

Testinny said:

...My PC is very old (2009) ...

...After trying FAT, booting with the USB drive says "Non-System disk Press any key to reboot" and I am still stuck.

Fat32 is the correct format to use. An old PC like this will have a Legacy BIOS, so you MUST mark the partition as Active else the bios won't find the partition to boot from on the USB. That can be done with Fdisk on a Mac. See step 3 here...

3. Set bootable flag on, start fdisk and enter the commands with red text....

Create Windows 7/8/10 bootable USB drive in macOS with command line (MBR partitioning scheme) – Oueta

Testinny · 05 Mar 2021

exFAT did not work, I let it run for 1 hour and 45 minutes. So I reformatted to FAT and tried to make the partition active with fdisk, but I still get "Non-system disk."
Even the process of making it active had some differences.
Here is what I did: I opened Terminal, found the number of the flash drive (disk3), typed "fdisk -e /dev/disk3"
and got the reply "fdisk: /dev/disk3: Permission denied"
After researching, it seems that people type "sudo" before the command to gain permission and be prompted to type their password so I did that.

Then I got "fdisk: could not open MBR file /usr/standalone/i386/boot0: No such file or directory"
but I still was prompted to type the red commands from step 3.

"Enter 'help' for information
fdisk: 1> flag 1
Partition 1 marked active.
fdisk:*1> write
Device could not be accessed exclusively.
A reboot will be needed for changes to take effect. OK? [n] y
Writing MBR at offset 0.
fdisk: 1> exit"

So it did offer me to type the things in red in Step 3 but what about that "could not open MBR file," should I ignore it? I then ejected the drive and tried it on my PC, but I got "Non-system disk." So I tried the fdisk operation again but this time I did reboot my Mac computer after typing "exit." Same results. Should I follow the further steps, that involve syslinux?

I will do the copying from the YouTube guide AFTER the fdisk operation, this time. It takes about 15 minutes to copy.
Update: it still does not work.

Update (January 7, 2021): Solved! Thanks for trying, I understand that it is not worth the headache, as these are not the Mac forums. I ended up borrowing a Windows 10 computer and got the USB to work in a few minutes with Rufus and it repaired the Windows boot file, now I can use my Windows 7 PC again.