Sony Ericsson :: Screen Either Black Or Muddled

I am hoping that someone can help. I dont know why buy my phone screen has started playing tricks on me, it either stays black (I can see that there is power to it but its not showing the normal screen), or it goes a bit muddled (lines though it, or it is off to the left or right, or only half screen is showing). Strangely, when it is staying black I can tell that it is working behind the scenes as if i tap the power button twice the screen powers off, then if i tap it again and press the bottom left it unlocks the screen (the screen looks like it has power but is still black) I can tell the phone is working as if i press the menu button it vibrates when i touch places where the menu options are. if i keep turning the phone off and on or locking and unlocking it will eventually work - but this can take anything from 1 attempt to 20 or 30 Then when the phone comes on properly it can go back to being black or garbled again in seconds or minuits, ocasionally hours.I got the phone less than a year ago (about 7 months - not long after it came out i think) - i have the box but no receipt.