Unresponsive screen? 4s

HELP!

I have an iPhone 4S (I've had it a month, my friend had it for year or two before me), with a broken lock button. Today I was using it and tried pressing the home button to get out of an app, it wouldn't work so I tried repeatedly pressing it and then I tried getting to the home screen through assistive touch, which also wouldn't work! So I just went to lock screen (through assistive touch) and now the phone screen won't do anything! Home button does nothing when pressed, and if I hold it down after about a minute Siri says "sorry i didnt get that (or whatever it usually says). I've tried connecting it to itunes on computer but an error message shows up saying its locked with a passcode (I've never had a passcode!!!). Tried charging it and everything, I tried calling it from a different phone (didn't ring, didnt show anything on screen).

Any suggestions or links to people with the same problem would be greatly appreciated