Dead PC HELP! Bad Corsair HX750?

So I get home from work today and my recently problematic PC will not turn ON*(edit). Pretty sure I left it on when I finished setting up the days worth of pr0n downloads and now when I try to turn it on nothing happens. I checked power cable, switches, flipped things on and off, swapped power cable, no luck. I don't get any lights on the mobo and nothing happens when the power supply switch is in the on position and the power button is pressed. I'm thinking this is a bad power supply. Any thoughts would be appreciated on what it might be and how to go forward with troubleshooting.

Should I use a DMM and check to see if I am getting voltage from the power supply? Would I even get a reading if the leads are not all connected to a chip interface?

I suppose it could also be the mobo but I figured it is probably easier to start with a power supply and go from there. The machine has been run almost 24/7 for about 3 years so I am not surprised at a hardware failure but I was hoping for some helping trying to divide and conquer.

Leading up to this issue I was having issues with the video card shutting off for no reason. The fans would go to max and the video would cut off and I had to restart to get it to come back. Temps were fine on the video card, it would cut off at the desktop when the machine was more or less idle. I updated the Catalyst firmware which helped for a brief period of time, maybe a few days, then it started not wanting to come out of "standby" or just not come back from the screen saver. I'm hoping this is not the video card having gone bad and fried my mobo. But I will find out soon...

I will post my build below. Any help would be greatly appreciated. Thanks!

1 x MB ASROCK|Z77 EXTREME6 Z77 1155 R

1 x Intel Core i5-2500K Sandy Bridge 3.3GHz (3.7GHz Turbo Boost) LGA 1155 95W Quad-Core Desktop Processor Intel HD Graphics 3000 BX80623I52500K

1 x G.SKILL Ripjaws Z Series 16GB (4 x 4GB) 240-Pin DDR3 SDRAM DDR3 2133 (PC3 17000) Desktop Memory Model F3-17000CL11Q-16GBZL

1 x VGA XFX|HD-687A-ZHFC HD6870 VGA XFX|HD-687A-ZHFC HD6870

1 x PSU CORSAIR| CMPSU-750HX 750W RT

1 x HD 1T|ST SATA6.0 32M

1 x SSD 128G|CRUCIAL

Take the psu out of the case and try jumping it to see if it will turn on. If it does then check the rails with a DMM. Here is how to jump it

Thanks that was pretty helpful. The PSU passed the test, fans came on. When I pulled out the main cable I found that one of the case cables had came unplugged but I dont know if I did that when I was unplugging the main from the PSU or not. Anyhow, it is turned on now so hopefully that was it. I did open everything up a few weeks ago to clean it but I didn't unplug much other than the video card to re-seat it because that was causing some issues which I think were resolved by drivers. Appreciate the help, thanks!

So it's working properly now? If so glad to be of service!

used to jumper them, but I bought a cheapo PSU testerhttp://www.amazon.com/HDE-Power-Tes...008025&sr=1-4&keywords=power+supply+tester+pc. works great to see if the PSU still works.