Boot Camp Assistant cannot be used

Hello,

I have a problem in Boot Camp, he stopped running suddenly when I try to open the message " Boot Camp Assistant cannot be used. This Mac does not support Boot Camp. "

I have a Mac Pro 2 x 2.4Gh Quadcore mid-2010

Yosemite 10.10.2

2 hard drives mac and use 1 HD now with Win 7 installed.

Always used boot camp and never had this problem . Already tried to change discs of all manerias and nothing . Does anyone have any idea what might be.