First post, be gentle...
Last night when I shut my ignition off, I heard something running under the hood...sounded like a fan or something that didn't shut off. I thought it would shut off by itself so I headed to my apartment.
Unfortunately when I tried to start the car this morning, the battery is dead. Any guess on what didn't shut off that caused the battery to drain?
Any advice would be appreciated.

 

well the fan would be the radiator (it has a mind of its own so don't worry about it) as for your battery, check the terminal connectors, i.e. move the wires attached to the battery shake them a bit, if it starts then after then you might need new connectors, or you could just polish them, the corrosion makes them stop working.

 

If your fan didn't shut off, then it could have drained your battery, and the fan staying on could be a bad relay. Once you jump started your car, see if the fan comes on right away. If not, then the problem with your battery is else where. Do what rival12 said for the connections, and take your battery to your nearest auto parts store to have it checked out.

 

Fan running after shutdown is normal for Accord. When coolant temp reaches ~225F, a switch closes allowing the condensor fan to run until switch opens.

You could have a faulty fan relay causing a simlar effect, however the fans would run until battery was dead.

I would recharge battery and check to see if fans are still running. If yes, then you know a bad relay is likely the problem.

good luck

 

Next time the problem happens open the hood and unplug the temp sensor in the top radiator hose.