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#11
I would install MiniTool Partition Wizard and use that to examine the USB flash drive. You will want to delete all partitions on the flash drive, make sure it is set for MBR type partitioning, and create 1 FAT32, primary partition on it. You will also want to right click on the new partition and click "Set Active." Make sure to click the apply button in MiniTool Partition Wizard.
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After doing the above, the Media Creation Tool should see the USB flash drive. You say you have the Media Creation Tool downloaded and Windows. Is the Windows that you have downloaded the ISO file that the latest Media Creation Tool just downloaded? If it is, then you do not need to download another copy of Windows just to make the USB flash drive. Just right click on the Windows ISO file, select Mount. A new virtual DVD drive will open, with it's own drive letter. Copy all the files and folders from the virtual DVD drive to the USB flash drive. That will recreate it for you without having to download a whole new Windows 10 at 3.5 GB every time you download it.