Snagged from a post, trying to figure out how to keep this info at my finger-tips.
You can try to hard reset it with buttons to see if it will respond but that will erase all of your data.
1. Pull the battery out and reinsert it
2. Hold volume down, home, and power buttons until the reset screen appears
3. Scroll down to wipe data/factory reset (using volume down) and press menu
4. There will be a lot of no's, and one yes. Highlight yes and press menu