You came here asking for help and you got at least three answers telling you that what you said in your OP cannot be done.
When someone finds this thread looking for answers to his own problems, it is of no good to give misleading information.
IF (and maybe I am wrong here), you flag your stick to make it bootable and format it to the appropriate file system, then mount the ISO and copy its contents to the stick, it MAY boot.
So, unless you know the exact procedure that you used to do AND describe it for us and the rest of the world, don't be an a** and keep saying that "it used to work like that; OR; my computers can do that".
This, times at least a hundred. OP, you saying you dragged and dropped a Windows ISO (or IMG file it doesn't actually make a difference in this context) from your hard drive to the USB stick and the USB stick then was able to boot into Windows 7 is truly stupid. That isn't possible. That's not how it works,
period. It's like saying you started a car that doesn't have a battary or an alternator. It's non-sense.
I signed up to this forum specifically to say this. Every time,
everytime I look online to try and find some tech support, or any support in general, I'm blindsided by masses of ignorant people who don't know what they're speaking of but insist on speaking anyway. It's truly maddening. It's maddening because it's some disgusting form of willful ignorance and incompetent malice. And it sounds like your problem was a corrupt partition table like someone said. Or, it could be the fact that a USB drive cannot boot an operating system via copy/pasting a disk image. Maybe your PC is set-up in such a way so that it recognizes the disk-image and automatically installs the operating system, but if that's the case, you should apologize for wasting these peoples time asking the same idiotic question over and over again until someone finally gave you a solution, which happened to be wiping the entire drive clean and starting from scratch. Also, I'm being an asshole because right now, to me, you are the embodiment of every ignorant jackass, from Yahoo Answers to even the most reputable forums, who, despite not knowing what they're talking about, deem it necessary and appropriate to answer anyway and in the process end up giving some poor soul an entirely incorrect answer or piece of advice.
Yeah, I understand there are different IMGs (they are IMGs, not ISOs), which you need to 'flash' onto the USB stick, such as some unofficial Chrome OS version with which I experimented in the past.
Ugh. Are you you actually trying to argue with these kind folk who are trying to help you even though you come across as a snide jackass? If anything you said actually made sense, fine, but all I've read so far is non-sense.
Guyd, I've got a problem. I had to reinstall windows and so I copied/pasted all my programs on my desktop onto a floppy disk. One of the programs was Photoshop which I need to do a school project. Anyway, IDK what the problem is, it doesn't make sense. I copied like 40 programs onto the floppy disk but not even one of them works, all that happens is it comes up with some error about not finding the file.. but I had just clicked on the file. Windows has really gone downhill I don't understand how they can release an operating system that doesn't even let you copy and paste programs. I feel bad for any business that has to deal with this, hopefully MSoft gets sued again.