My Macbook Pro can't install Windows7 On any MAC OS
Your Windows 7 DVD probably is defective. Either that, or the optical (DVD) drive is defective. I assume you are using your internal optical drive. If not then, then the external optical drive is defective or may not be compatible.

I assume you your firmware is up to date. Although, on a 2011 model, this should not be the cause of your problem.

Try this. Insert the DVD in the optical (DVD) drive. Restart the Mac and hold down the option key. A DVD icon should appear with the label "Windows". Select this icon and continue booting. If everything is OK, then the Windows installer should start. (If prompted, you may have to hit the space bar on the keyboard.) I assume the installer will not start, thus indicating either the DVD or the optical drive is at fault. If the installer starts, then exit and post a comment below.