Coolermaster GX 750W is a lower quality PSU compared to the Corsair 650TX. And the Corsair 650TX is sized right for your system.
Your PC's power actual requirements should be under 400watts at full load, under 200watts at idle.
So there is something else going on in your case.
What cables did you unplug in your case to get it started with the Corsair PSU?
That's more than I can say for the OP's DOA Corsair.
He didnt say it was DOA. He actually got it running by unplugging some cables inside his case.
If he has something else going on inside his case he might have the same problem with ANY power supply he hooks up.
damit why didnt i test if wiring the on off switch the other way round worked before i sent it back, well i did wire it the right way; with the green on the + and the white on the plain pin.
I have run 2 other power supplies on the same pc and i didnt get any problems, iv used the ocz stealth extreme 600W and the akasa power pax 460w and both work fine with no trouble at all with just 2 hard drives.
I thought it might be to do with atx 2.2 adn 2.3 but why is my power pax 460 psu which is 2.0 working?
the Cosair PSU cabbles i removed from the mother board were the 24 pin and the intel 4 pin
pluging them back in woul let the pc start up.
however shutting down and returning after an hour would have the cosair fail to start up.
I find it weird WR2 that you say
"Your PC's power actual requirements should be under 400watts at full load, under 200watts at idle"
as reviews say the the gtx 470 consumes around 400w during load.
and there are all the other 5 sata drives.
That was 400watts for the WHOLE system - not just the video card. That 400watts is measured at the wall socket and its 400watts AC. PSU use that AC input to make DC power for your parts and if a PSU is 85% efficient that 400 watts of AC is making about 340w DC power for that test system. PSU are rated in DC power they can provide to the PC parts, not in how much AC they draw from a wall socket.
A HDD takes about 10watts max and usually a lot less if not in active use.
If you want to see what the video cards alone use in power check out this data @ TechPowerUp
also i cant get my 460w to start up with all my components on.
Since the startup idle loads should be under 200-240w I still think something else is going on in your case. 460w PSU should be plenty of power to boot to idle even if it can't run things fully loaded.