It's a hardware problem - needs a heatgun and a phillips screwdriver to sort it out. Can be repaired in an hours. Mine's presently in pieces on my desk at work, not had time to sort it out yet

The fault stems from how the main processor and graphics processor are connected to the main board. They use a system called a BGA - Ball Grid Array - basically, every single 'pin' on the underside of the chip is connected to its associated 'pin' on the board by a small ball of solder. The solder's not brilliant to start with in order to cut costs, so what happens over the course of hundreds of heating and cooling cycles (ie, power on and use, then power off), the balls of solder either crack, or break contact between the board and chip on one side, making the device useless because the chip's now effectively disconnected from the board.

By heating the chip and board carefully, the balls of solder melt ever so slightly, allowing the chip and board to become fully reconnected again.

If you have some patience and a heat gun, do it yourself (worked for me!). I'll dig up the links to an awesome 3 part guide on youtube to save being bum-raped by an ebay seller charging you for the same, or a shop charging a small fortune for the privilege.