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I don't know what to say right now since I don't know the problem fully without any evidence, but here I go.

Do you think in the time where you left your macbook charging anything WOULD have happened to the macbook/charger?

Do you think when you left your charger (I think..) at your dorm that it might have hit something (a wet/hard part maybe?) and caused any sort of damage to it? What about your macbook (and vice versa)?

Do you think while you were studying you might have hit your macbook on the way or that maybe without you noticing someone might have done SOMETHING to your macbook?

I don't know but usually when the charger doesn't charge the macbook its more of the battery being screwed up from over-charging, and/or the charger being messed up in some way and when connecting to your macbook charges normal, that later when you try to charge it it doesn't charge is because since it was messed up the electrical currents it sends through are not as 'clean' and would eventually mess up your magsafe port and/or battery. I learned this from my neighbor who is a computer wiz at macs and pcs.
 
Before you go spending $700 to repair the thing, try borrowing someone else's battery. Try the mag safe plug with the borrowed battery and see if it charges. If so, you've just got a crappy battery, and a much lower repair bill.
 
If all else fails, try selling it on eBay. Fully disclose all information! You might be able to get quite a bit for it. Then take that plus the $750 you were going to spend to fix it and get a brand new Macbook.
 
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