Big problem please help!

I cannot unlock my iPhone. When i went i eather press the lock button or the home button nothing happens, and when i try to put it on vibate when it is locked nothing happens. When i plug it into my pc the “slide to unlock” message shows up and everything works perfectly. Also itunes does not see my phone but my computer does. When i take it off the charger the “slide to unlock” screen apears again and it works fine. It just doesnt work when locked… can anyone help me?