First, try closing down all running apps:
Double-tapping the Home button will bring up the running apps icons along with an app screenshot "card" above the icon. Tap-drag the app's -card- (NOT the icon) up and off the screen.
Next, try to reset the device:
Device Reset (won't affect settings/data/music/apps/etc)
1. Press and hold (& continue to hold) BOTH the Sleep/Wake button & the Home button.
2. Continue to hold BOTH (ignoring any other messages that may show) until you see the Apple logo on the screen.
3. Release BOTH buttons when you see the Apple logo and allow the device to boot normally.