iPhone- black screen, reboots on own, will not start

Hi! HELP! I updated my software yesterday or today (cannot remember) to iOS 7.1.2, and now my phone keeps rebooting itself after it automatically locks. (I dpn't know if the software update is related to my phone not working) The screen turns black and nothing is on the display, however the phone is still on. I can occasionally hear incoming texts, also when called, phone does not go straight to voicemail. My iPhone will occasionally let me restart it by holding down the home and power button. If I get the phone to work and come on, I cannot lock it, otherwise this problem starts all over. WELL, I accidentally made the mistake of locking it, and now it won't do anything! Also, phone is not recognized by iTunes! Pleeeeeeeeeease help 🙂