Hello. That normally means just restarting, or pulling the battery first if the screen has frozen.
To access the recovery mode to just reboot, or wipe the cache partition, in case your screen is not responding:
Hold Volume Up - Power - and Home button together until you feel it vibrate. A horizontal Android and a selection list will appear.
Just press power while the reboot choice is highlighted by default, or use the volume buttons to scroll down to wipe the cache partition (which is a useful type of house cleaning).
You can factory reset from here also, which will wipe all your data, but if you select it accidentally it will make you select more options as a safety measure.
Doh! It would be a good idea, if the software allowed it, if when members try to answer a post, a flag comes up if another member has already started to answer it.