It is my understanding what the Windows flash drive installer created using Boot Camp can only be used on select Mac computers. The flash drive can not be used on PC's. This post Will bootable usb created by bootcamp on mac work with PC? describes the same problems you are having. (Look for Technicallity's solution.)
The iso file you have can be setup in one of three ways. First, is a legacy BIOS boot which usually assumes the use the MBR disk partitioning scheme. Second, is a UEFI boot which assumes the use of a GPT disk partitioning scheme. Third is both types where you are prompted to select your choice when booting. If you need to changing the boot setup, that I can help with. For example see here.
It would be easiest to have another Windows machine available to create the bootable flash drive. I assume you don't have one?
Based on the limited information you have provided, here is how I would proceed. (Don't feel bad, no one ever gives me enough information.) This is a rough outline.
- Get a machine running Windows to assist you. That you already have. It called your Apple. Assuming you do not have a Fusion drive, it is relatively easy to install and later remove Windows from any Mac computer. For your Apple, I do not have enough information to say how easy. I would install but not activate Windows. This will give you 30 days of free use. You will then be able to use the same Windows 7 to install and activate on your new PC.
- Get and use the official Microsoft tool for creating Window 7 installation flash drives. The tool can be found at Windows USB/DVD Download Tool. Don't let the name fool you. The tool does not download software. It is used to create bootable install media after you have downloaded Widows 7.
- Determine whether you are going to use a legacy BIOS or UEFI boot method. From my understanding, if the UEFI option is available, you have to configure the boot setup to select it. (I have never seen an EFI boot. I have always used the legacy method.)
- Determine if your iso has to be modified using the Microsoft oscdmg.exe tool. This tool is used to change the install boot method.
- Create the bootable flash drive and install Windows on your new computer.
Anyway, I figure I am right only 10% of the time. Most likely someone else will have your solution. If you have further questions or would like to proceed, add a comment below.