You flipped the switch that reverses the throttle channel.

The ESC has a automatic safety that will not give you control of the motor until it recieves a ZERO throttle input from the TX first. This is to prevent the thing from going wide-open if your throttle stick isnt where its supposed to be when you plug in the battery.

When you reversed the throttle channel, now everytime you plug the battery in, the ESC sees the TX signal as FULL throttle. Since the safety is built in to not let it turn on until it gets a zero signal, it just sits there waiting on you to return the throttle to nil, before it allows you to control it again.

Look on your transmitter, and flip the switch again for the throttle.(hint - its normally channel 3). Then get a good grip on your helicopter, and plug the battery in. Now while still HOLDING THE HELI, advance the throttle a little bit...it should be returned to normal.

You could technically fly it in reversed mode. Just move the throttle all the way up(what normally would be full throttle), then plug the battery in on the heli, and then start moving the stick down for more throttle instead of up. It basically reverses the stick input required for throttle. On a side note, this is not recommended.