I can't install or remove windows 7 or later using Boot Camp Assistance?

I tried fro couple days to install Windows 7 on my Mac book pro which has OSX Yosemite (10.10.2). A you see in the capture, the third checkbox is disabled. I create a Windows 7 on a USB flash and downloaded the latest Windows support software from Apple, All I have to do is install it on the mac.

What's the problem here, please help?