How do I change my form of security without losing all my data? (story inside)

[AC Question]

So some back story: I set the phone down last night for a few minutes, and when I came back the security on the home screen had changed from the connect-the-dots pattern to a pincode. I don't remember setting a pin when I set up the connect the dots, but I have tried all the things I would normally use and so far nothing has worked. I've had the S4 for about a year and it hasn't given me any trouble until now. Recently, the storage has gotten pretty full, but I don't know why that would have anything to do with it. Even more puzzling, when I plug it into my computer it recognizes the device but says there are no files on it which, of course, is simply not true. How do I get around this problem without losing my data?
Thanks for your help!

 

[Rukbat]

Bring it to the carrier and they can change the lock screen to None (by working through the USB port.)

For obvious reasons (unlocking a phone someone "found"), we won't give out the details.

It's possible, BTW, that your phone glitched, and wiped everything. That's why everything should always be backed up off the phone.