I sent my head unit off to GTS intermedia services to be refurbished and it's been fine ever since. Mine was doing the same as yours. Turning itself on and off at random.

I paid £55 to get mine sorted but if you look at the second page of the post there have been a few changes to the company that refurbishes them. By the looks of it you will need to sort your own return postage.

This is the link you need:

http://www.seatcupra.net/forums/showthread.php?t=107055