iPhone 4s keeps locking itself

My iPhone 4s randomly started locking itself and prompting for a shut down.

My warranty is up so I can't send for a new one, and this problem makes it extremly hard to use my phone, and suggestions as to what I can do?

So far I have updated, turned off/on. pressing the lock button repeately and trying to wiggle it around. I really don't want to resort to a system restore as I just purchased a new laptop and my iPhone is not backed up to it yet, so if there is anything I can do before that option please let me know! thank so much.