Maybe a little late of a response, however... Ive had the p-7805u for quite a while. I had the same problem which I noticed that was triggered specially by old games rather than demanding games like Crysis. In fact, the computer never gave me a problem on the most demanding gpu applications, but crashed within minutes in games like Warcraft III. The screen showed artifacts, crashed and then recovered giving me the "driver has recovered" message, and ultimately and almost always hard froze after a couple minutes. I was getting really frustraded, even got an rma for warranty service, but didnt send it in because i couldnt survive without a computer at the time being.
I started monitoring my gpu clocks. Almost all gpu's, being more dramatic in mobiles, lower their clocks when they are idling. I finally noticed that the computer started artifacting and crashing when the clocks lowered for idling and lower energy consumption purposes. Simple solution: download desktop drivers from www.latopvideo2go.com
, any in the 19x.xx branch, and use their modified inf so that you can install it in your laptop. In the nvidia control panel go to 3d settings and under global change "Power management mode" to "prefer maximum performance". This doesnt allow the gpu to lower its clocks, solves the problem permanently =). Ive run crash free for months, and battery life is only lowered by maybe 10 minutes, which you can always prevent by changing the setting when you plan to go on battery.