Grey loading bar

This problem came up back to december and i've already posted plenty of threads back then, but my problem never exactly got solved and I think it's kind of pointless bumping up old threads.

In short, when i start up my mac, this shows up:

The bar "loads" for about 20 minutes, then right when it's at the end my computer just shuts off.

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I know my hard drive is perfectly fine, i'm on my mac right now (on bootcamp). I can fiew all my files on the 'mac side' of my computer, and on my 'windows side' everything looks just fine.

I have no idea why it started doing this, back in december when it started happening i did absolutly nothing different than i normally do, and I didn't even mess with any boot up files or anything, so I'm not exactly sure why it's doing this in the first place.

Also, when i do COMMAND + R during startup and select re-install mavericks, the drive or whatever that pops up is bootcamp, and when i try to select it, it just say that it's locked.

At this point i honestly don't really care if any of my data gets wiped, just as long as bootcamp remains fine. It's extreamly late here right now so if i forgot anything or if you need any more info, just ask.