its not the gpu due to it only crashin when the cpu is overclocked plus it did the same with my x1950
iv done it for a few hours where like i sed the game crashers in 10 to 20 mins
Assassin creed is a console base game so it will push your cpu to the limet, So im guessing your cpu is overheating while playing that game, The reason why your pc dont crash while playing other games is cos there pc based games right? and they dont push the cpu to the limet. or the other games you play dont push the cpu to the limet. get a better cpu cooler.

Also remember running orthos wont cause your system to get as hot as playing a game, cos when you play a game you have more heat from your graphics card making you case warmer causing your cpu to run hotter then if you just run orthos.
I had problems with this game also, I think it's the "call home feature" that tries to connect to Ubisoft, if you disable your net connection before playing it should fix the issue...
Worked for me anyway, had constant crashes till I disabled my network adapter prior to playing the game
tryed cleanin it so im thinkin of geting a new case with better cooling at the min i have theI had exactly the same, game crashing after 10 minutes or so, finally narrower it down to the cpu overheating and reaslised I hadn't cleaned it an a while. Removed an impressive amount of dust from the heat sink and then played the game for an hour or so fine.
tryed cleanin it so im thinkin of geting a new case with better cooling at the min i have the
Antec Sonata III
(and Sleepery you can punctuate my post if you realy want to waste your and my time not my falt im dyslexic)

AFAIK a Dyslectic can also not see the typing errors on the screen he typed inCorrect me if I'm wrong but surely dyslexia is where you are able to spell but the letters get jumbled up in your head. That is quite different from being crap at spelling and grammar...![]()

His GPU is at stock all the time, the only difference is an overclocked CPU, when overclocked it crashes, when at stock it runs fine = CPU problem, either too hot or too little VCore to run stable.those grafics card can run very hot much so make sure its not that running to hot
AFAIK a Dyslectic can also not see the typing errors on the screen he typed in![]()
(Or it could be that Rivatuner is working)
weird.