Seems odd that you were doing a firmware update on the Hero 2 considering the last update was released in 2013. I'm guessing you were having issues with the camera already and thought a firmware update may fix the issues?
If the camera is not powering on, it could be knackered. Try removing the SD card, battery and plugging it into the USB cable and powering it up. If it doesn't come on, the unit is well and truely dead. If it does power on. Power it back off, put the battery in, try powering it on again. If it doesn't power on, could be a battery issue, if it does power on, then power it off, put the SD card in, try powering it on. If it doesn't power on, it's an SD card issue.
Also, with it plugged into external power via the USB, hold down the power button for 10 seconds to perform a system reset, this will boot from the last known good image and not any temp firmware.
