First thing I can think of is that maybe you have an app that is conflicting with your software on your phone.
Have you had any apps that have updated recently and you have since had the problem? (EDIT: SORRY, I SHOULD HAVE READ ABOVE FULLY BUT SOME APPS UPDATE AUTOMATICALLY)
There is a trial and error process of removing every one one at a time, waiting and seeing if that fixes it.
Alternatively my preferred option is a full reset and put the apps back on one at a time.
I'm not saying my method is best and there are a few who will agree with that but sometimes it's good to have a clear out and start again.
First off you'll need to make sure your phone is backed up. Don't rely on Kies but there are a couple of good backup programmes available on Google Play like Titanium and My Backup.
If you're not worried about losing your text messages, photos, music, emails etc..., and your contacts and calender are already sinced with a google account you can then go onto the next step.
This next step is a full reset of the phone it will wipe everything...
Go into dialer and type *2767*3855#
Once you've done this your phone will wipe everything in the memory and return the phone back to factory settings.
You can then put your apps back on one at a time with a sensible time gap between each, until you find out which one is causing the problems.
If all else fails and you don't want totry the above you can always take it to a Samsung repair centre, these can be found here http://www.samsung.com/uk/support/location/support
