Method #1
Then turn of Strict Mode. This mode makes the screen flash when certain applications are using a lot of system.
Method #2
Simply hold down the power button for 10-20 seconds to soft reset it.Method #3
Press and hold the Volume Up + Home + Power button simultaneously to hard reset it. Then, when in recovery mode, select Factory reset.You can also go to Settings -> Back up and reset -> Factory data reset -> Reset device -> Reset everything. Be sure to BACKUP your device before doing this, since it will wipe you phone clean. This is a last resort method.
All three of these methods have been known to resolve the problem, but the first method is the easiest and should be your primary option.