iPhone call glitch

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I recently purchased an iPhone (about a week ago) and it was working fine. Two days ago, weird things started happening. EVERY time i end or reject a call now, it makes the sound effect of taking a picture, then goes to a black screen like in standby, and instantly requires me to re-enter the password. It was not doing this before, but is also not the most severe problem. Every so often, also when ending or declining a phone call, the touch screen will just flat out stop working and will not respond to anything until I do a hard reboot or sync. Sometimes the touch screen works to slide the unlock slider, but the keypad will not respond for me to enter my pw.

I guess my question is, is this a hardware problem? Should I go back to the store? The thing is only a week old... or is this something that can be fixed by wiping it clean and re-syncing? Has anyone else experienced anything of this nature?

 

[Earless Puppy]

First I would do a software restore
Second well maybe first, try using your phone without your case see if that fixes it, although this would not make the lock sound if the sensor is blocked it could make the screen go black and be unresponsive