harddrive failure

i recently tried to upgrade to el capitan from yosemite. it failed during installation process, and now everytime i boot up my mac it takes me into disk utility. i cant erase, restore, mount/unmount my osx partition. i took it to the store, they checked and it was harddrive failure. im just wondering how am i still able to run windows on it. i can boot into window normally and everthing worked.

macbook pro early 2011