Thank you all very much for your help and assistance !
Most probably is my Power supply .
The One that i have is Thermaltake PSU ToughPower XT/Modular 875 W !!
I may need as FusionHorse suggested 1000w , or on the other hand maybe my Cooler is the Problem here !! Today i saw Temperatures when i run my Msfs from 65C up to 90C !!
The One that i have is Thermaltake Frio CPU Cooler 12025mm Fan .
But No Pc Shutdown !!!