BOOTCAMP startup disk not showing up (PLEASE I NEED IT ASAP)

Your iMac (21.5-inch, Mid 2011) - Technical Specifications needs to use it's built-in Optical drive (DVD/ CD) to install W7/W8.1. W10 is not supported by Apple. However, you can upgrade W7/W8.1 to W10, if you really must.

• Download the ISO from https://www.microsoft.com/en-us/software-download/home
• Burn the ISO to a blank DVD-R SL disc of reputable brand
  • Right-click on the ISO and select Burn
  • Expand Burn dialog, and choose Verify and Mount
  • Choose the lowest Burn rate
  • Click on Burn and verify
• Click on Download in BC Assistant and download Windows Support Software to a USB2 Flash drive. Do not use any other drive types
• Disconnect the USB2 Flash drive
• Run a SMC and NVRAM Reset
• Insert DVD, run BCA and click on Install
• Use the Windows icon (not EFI Boot) from the CD
• Try to install W7/W8.1

• Assuming you have installed Windows and it is working, you can install Paragon NTFS on the macOS side.
• Download BC Drivers using BC Assistant and Download option.
• Copy the contents of the USB3 to a folder on the Windows partition which you can remember.
• Boot into Windows, and go to the folder in the previous step.
• Run Setup.exe

If you do not have a USB2 Flash drive, use Paragon NTFS Trial version, copy the contents of the USB3 to the Windows side, and then install BC Drivers.