Black screen issue on EAH4850 1GB xfire

i was playing Age of Empires III The Asian Dynasties, my monitor suddenly blacks out, the whole system locks up. The only possible thing i could possibly do is hard boot my PC. For every other game it works fine ie. CSS Crysis WOW, could it be the directx problem? driver?
Whilst playing Aoe i am sure that the temps of the GPU is round 60c

My system
Core 2 Q6600
DP45SG mobo
EAH 4850 1gb x2
800w PSU
4GB DDR3 RAM

Thanks

Danny