Themastererr :
It's possible the Power Supply does not have enough juice to start the GPU, but your system has 460 which should be enough...
When a computer starts up, it's not under full load. Load is very very small, minimal; it is in idle. Also, the misconception that a power supply "has juice" and can "run out of power" needs to be cleared. A power supply will not hit a limit on power. A power supply will not run out of power ever. What will usually happen is it will burn before that ever happens
or a protection circuit will kick in and shut it down. It requires a specific power supply design, a specific, customized load, and overridden protections for a power supply to ever "run out" or "hit a limit" on power, and even before that is ever reached, the voltage outputs would get too low and your computer would be possibly damaged.
The power supply does not even store the energy that the computer uses; it comes from the power plant. The power supply simple converts the electromagnetic energy into a different form and distributes it to the computer. Nowhere though will a power supply ever "run out of juice". A power supply is
not a squirt gun but is an energy conversion and distribution system. Power is the rate at which energy is transferred or converted BTW.
Only a continuous current power supply will always have a power limit. Such as a light bulb connected to a battery. But a computer power supply is totally different and does what is demanded of it.