you're not going to like this...
you are not alone in experiencing this problem. I have just bought a brand new f series vaio and i have had this problem right out of the box. I have done some research and i'm sorry to say there is no quick fix.
the problem is caused by what is called a TDR (timeout detection and recovery) basically your graphics card is taking longer than expected to complete a task, windows recognises this and stops the process, resulting in your graphics card restarting (this is why the screen always goes dead just before the notification pops up) the good news is that in days gone by before the TDR system was put in place the computer would have just crashed completely or given you the blue screen of death. so if there is a bright side to look on, it is that in most cases you can carry on working/playing without losing any precious data.
The down side is that there is no single cause for a TDR, it could be anything from faulty RAM, to a driver conflict. If, however, this has only started since the computer was returned to you from sony, I would be taking the matter up with them, but given the horror stories i have heard about sony customer service i wouldn't be holding my breath....
