No Windows 10 Option on Boot Camp, Only 7 and 8

Your 2011 Mac should be using the built-in Optical drive and a physical DVD, which means that this file must be added to the W8.1 ISO and burned to a physical DVD. If you put this file on a USB flash drive, it will not work.

Do a backup, using either Time Machine or a cloning program, to ensure files/data can be recovered. Two backups are better than one.

Try setting up another admin user account to see if the same problem continues. If Back-to-My Mac is selected in System Preferences, the Guest account will not work. The intent is to see if it is specific to one account or a system wide problem. This account can be deleted later.

Isolating an issue by using another user account

If the problem is still there, try booting into the Safe Mode using your normal account. Disconnect all peripherals except those needed for the test. Shut down the computer and then power it back up after waiting 10 seconds. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. When you reboot normally, the initial reboot may be slower than normal. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart by using the application un-installer or by using the developer’s uninstall instructions. For each disable/delete, you will need to restart if you don't do them all at once.

Safe Mode - About El Capitan also Sierra

Safe Mode Startup – El Capitan. also Sierra

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. On the screen with Options, please open Options and check the bottom 2 boxes before running. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.

Etrecheck – System Information

As noted in Use Windows 10 on your Mac with Boot Camp - Apple Support, W10 is not directly supported on 2011 models. However, you can install W7/W8.1 including Bootcamp drivers, and then upgrade to W10 Anniversary Update with an in-place upgrade. Creators Update has some additional challenges on Macs.

You can install W8.1 and leave it unactivated, but fully functional. Upgrade to W10 in-place, and then use the W10 Product key to activate. Once W10 is installed and activated, the licensing signature of your Mac is registered with Microsoft.

Please be aware that any re-installation of W10 must also follow this method, otherwise you will not have proper working drivers that W8.1 provides.

Turner-Garnettes wrote:

Are there any other ways to do so that you know of?

Using https://technet.microsoft.com/en-us/library/hh824952.aspx, you can create a file called ei.cfg, which uses Channel as OEM. This should allow you to install W8.1 without a Product Key temporarily, till you get W10 installed.

Can you verify the file name on the ISO you created? Windows Notepad will typically add a '.txt' at the end of the file name, if it is used to create the file.

On the new ISO that you created, can you check the full file name of ei.cfg using a CMD window, not File Explorer?