Macbook Pro boots into Windows when selecting Macintosh HD

So I am unable to get my Macbook Pro to boot into OS X at all. When holding down Option during boot up I select "Macintosh HD" as my drive, but it still boots into Windows. In Windows Boot Camp utility, I choose Macintosh HD as my startup disk, reboot, but it still boots into Windows. I haven't tried booting from my install disk as it is at home right now and I am at work, but I'll be trying that soon. Thanks for any help!