2011 MacBook Pro Stuck at 50% Boot

I had not touch my Mac all day until I came home that night. I didn't not shut it down completely but that is what I usually do I just put it to sleep. So I wake it up and login into it, it let me login but that's when everything started to move slow so I let it sit there. I came back after 15 minutes and tried to use my Mac and that's when the spinning wheel came on the screen so I let it set for 20 minutes and it was still there so I just powered it completely down. And now when I try to power it back up the Apple symbol plus the loading bar comes onto the light gray screen but the loading bar will not go pass 50%. It has been like that for 2 hours.