Is this a "Vestel T816"?
I used to have one abouit 2 yrs ago and it did this, (they all do it!!
Turning it off is not effective, you need to remove the power plug and wait 5 minutes or so then plug it in again and it should boot up OK.
Could try here click here for more help, but time's moved on and there are even more up to date and equally unreliable units being wrestled with! lol