Sorry about my terrible research i was looking at the regular GT 430 and not the one you had. It could be temperature issues with the machine. download GPU-Z http://www.techpowerup.com/gpuz/
and run that application if you can get it to run before your machine has instability issues. If the card hits close to 95 degrees celcius or higher that would most likely be the issue. If you have 460x2 it should be sufficient to support that card but with the 460x2 i do not know how the power is distributed across the system. GPU-Z will also give you wattage information and other things regarding the GPU. For further research in temps / power you can download HWmonitor which will tell you the temps of all components of your system (If they are supported). Also try some older drivers such as around the 275 series of them to see if you can narrow out if its a driver related issue.