I wanted to install PopOS on my laptop, so I downloaded the ISO, used balance etcher to flash it onto a USB drive, and then my computer wouldn't recognize my drive at all. I tried to boot from my drive but it gave me the "failed to open efi boot mmx64 efi not found" error. Now I can't use my flash drive and I cant install Linux. I've looked all around for solutions, but there aren't any that work for my problem. So after this I tried to use DISKPART to just start over and try again but it says that I cant clean it because of "diskpart has encountered an error: access is denied." and then I tried to clear the formatting and many other methods to fix my drive, but nothing has worked. I know this is a big question with a lot of random variables, but I'm not super experienced with all of this and I am looking for some help. Any ideas how I could go about this?

try rufus to put the iso onto the usb https://rufus.ie/

I don't think your flash drives are ruined - if you want to use them as storage you just need to re-format them; if you want to use them to create a bootable installation/live medium, you have to do that properly.
Instructions are usually found on the distro's web pages - here.
Are you doing this from Windows, or from another Linux install, or something else?
It looks like Pop_OS recommends balena (not "balance") Etcher for most cases. I recommend you try again and pay more attention. But rufus is also good. Or dd.

I do not know what "DISKPART" is.

Hi JtheBlueEnder,

Welcome to LinuxQuestions.

Although it is not 100% clear, I am getting a sense from the error you are reporting that there may be a mismatch between your target computer's firmware setup (BIOS or UEFI) and the way you formatted the external USB drive from which you're trying to install PopOS.

As recommended above by ondoho, I would be inclined to repeat the process of creating the USB installation medium with Etcher. However, make sure you know what the firmware on your target computer is (BIOS or UEFI) and use the appropriate choice in creating the installation USB.

@ondoho : DISKPART is a Windows partitioning utility.

@JtheBlueEnder : I would not try to create a USB installation drive for a linux distro using DISKPART. As mentioned by ondoho, each distro usually recommends a method / tools : follow those instructions. Although I am unfamiliar with PopOS, it seems from the above information that it recommends using Etcher, so you at least have the right tool. Just pay close attention to the UEFI (or EFI ... same thing) / BIOS distinction.

Let us know how things go.

Rick

Rufus in the default mode will will make the usb writable again by clearing out the partition table of the usb, create a partition formatted fat32, copy the contents of the iso to the partition, install syslinux bootloader to the mbr of usb. Some iso's work by this method, while others work by using dd. I think balena-etcher does somthing similar to dd. Rufus also has a dd mode.

I have made a few USB disks for Pop_OS! using Rufus, it works perfectly, per colorpurple21859 said.