Still on but dark screen, some twitching, randomly.

My phone was in an otterbox for it's entire life, purchased over a year ago. No insurance. Yesterday it decided to sometimes go dark but still be on. When the screen is on, I can sometimes see twitching. Do I have a soon to be 400.00 paperweight or is there a solution? Factory reset from itunes yesterday. Resetting by holding down the home button and on/off button only sometimes works. Please help.