You have burnt out the Graphics chip on it, i am amazed it has lasted this long as these model are prone to gpu failure.
Under the gpu there are small balls or solder prob 200 of them and a few have melted and joined together shorting out the chip or the heat has lifted a section of the chip, same result dead gpu.
Wrapping it in a sweater just heats up the solder until it turns back to a semi fluid and the solder balls reflow back to the correct position.
Pressing on the keyboard also does exactly the same thing as in that instance the chip has lifted and you are just pressing it back down.
Eventually the solder will fail completely as HP are renowned for using cheap chips and even cheaper solder ( other manufacturers are also available).
You need to have the gpu reballed or replaced, NOT reflowed.
The HP DV, TX, CQ and now the G6 and G7 series all suffer from gpu failure.