Macbook Pro late 2011 Boot Camp

Hello,

First of all, i'm sorry for my english.

I would like to know if it is possible to install Windows 7 on my late 2011 Macbook Pro.

I've tried trough bootable USB, and bootable DVD but no success.

When my mac reboot it shows that i don't have any image or something like this.

Should i buy an external optical drive and plug at USB port? my Macbook have an internal optical drive?

I hope some of you guys can help me.

Thank you!