I deleted something important (Mass Effect 3)

I was trying to make some room on  my hard drive by deleting stuff that didn't seem very important, and now when I try to play Mass Effect 3 it says disc unreadable. So I went to www.xbox.com/support for some help. For some reason Mass Effect 3 works when im not signed into my gamer profile. Im really confused so any help or info would be appreciated.