I'm having trouble finding a decent pic of your card but from what I did find it appears to have a 12v power connector, could you confirm this is correct and if it is correct is this supplied solely (no other devices) from a dedicated power lead?
What driver are you running for your card? in the nVidia control panel is the gpu temp monitor, could you give us your temps? (right click desktop, nvidia settings, select monitor, then temperature settings)
Regarding local power where you are, is it the domestic power you're using or generator supplied?
EDIT: I have yet to see you mention the stop error report so I'll assume you have your pc set to restart on system failure, open system properties, either through control panel or right click My Computer, select the advanced tab, then at the bottom select start up and recovery, in there uncheck "Automatically restart". This should display the dreaded BSOD when your pc crashes instead of restarting directly to windows, also check your event logs to see what is in there, right click my computer select manage, then event viewer under system in the tree on the left.