That questionable Arctic Power 600 Watt PSU is probably only capable of supplying no more than 20 Amps on its single +12 Volt rail. Read the label on your PSU.
The overclocked GTX 460 will draw more than 13.5 Amps from the +12 Volt rail under full GPU load.
That doesn't leave you with sufficient current capacity on the +12 Volt rail to power the remainder of the system (motherboard PCI-E slots, HDD's, CD/DVD drive, etc.). These days the current capacity on the +12 Volt rail(s) is the primary consideration and PSU wattage is secondary.
You need a good name brand PSU and Arctic Power is not one of them.