Hey Ravisp,for the camera issue,try clearing out the app's cache by going to Settings->Apps->All and then tap Clear Data.This will set your camera to default when the first time you bought it.For the notification prob,STAMINA MODE will only notify any events once and then it will turn off to save battery.So if it continue to blink for a long time,try disabling the LED notifications,switch the phone off and restart it back again.For the media player stopped working,it stop because you might set a ring tone for that particular notification but you set the Ringtone Volume to low or mute.That causes it to stop the media player automatically.All in all,you can always do a hard reset to put your phone back to normal setting.
Sorry if any of those doesn't help you,but i'd try my best.Cherrio