Sorry to read of your problem. But don't panic.
1. Try a cold boot (hard reset). The process is linked from my FAQ & help link, below.
2. If that doesn't work, try a long (up to 60 second) press on the power button. If that does reboot the device, do the cold boot & then uninstall that app.
If neither of those work, given the age of the device, then just get it exchanged.