I have a 580sli set up with the Gen3 version of your board.
Here are my specs.
Intel i7 2600K @ 4.2 Ghz
AsusP8Z68-V Pro/Gen3
16GB Corsair Vengeance Blue 1600Mhz RAM @1.5v
HAF X RC-942 black full sized tower
Corsair HX1050
Corsair H80 Liquid Cooler
1x 240Gb OCZ Vertex 3 Sata 600
1x 1TB WD Caviar Black WDFAEX1002
LG SuperMulti Blue BH10LS30
Scythe Kaze Master Pro fan control KM03-BK
2x MSI n580GTX lightnings in sli
Windows 7 Ultimate 64 Bit
You said the fans turn on. Does that include the graphic card fans, or are you only talking about the CPU,PSU, and case fans? Anyway, according to the information you supplied, I tend to agree. This could be, initially, a PSU or mainboard problem. I say, initially, because an insufficient or faulty PSU can, in some cases, cause other damage.
Also, here is a link that may help in choosing a PSU, if indeed, it is either faulty or insufficient. A faulty PSU or mainboard or an underpowered system isn't always noticable right away. Anyway, skip down to the part where they recommend wattage for a sli set up of those cards. I checked a few other reviewing websites as well. They are also recommending the same wattage.
http://guru3d.com/article/geforce-gtx-470-480-review/13
Did you change anything shortly before this happened? Update Bios? Is/was your system and/or the graphic card oc'ed or in turbo mode? Try hooking up a different, but fully functioning PSU to your system with either the same or higher wattage, or hook up your PSU to a different set up using similar wattage. You may or may not get a chance to do this, but pay good attention after pressing power on, to see which mainboard lights are on. and listen for beeps. If you don't hear any beeps, make sure the speaker is attached to the board properly. If your board is functioning correctly, the lights, and especially the beeps, should lead you to the problem within seconds. (If necessary, refer to you manual for beep explanations) If nothing happens within 30 seconds of power on, then the system may have failed a power on test. At that point, you may want to check to see if the clear rtc(clrtc) jumper is still in place and in the normal(default) position? If not, it won't boot. Then, you may want to recheck all board connections/switches again. After checking these connectors, and if you ruled out the PSU as the source of the problem, you may want to contact your retailer. Believe it or not, these simple suggestions have solved quite a few similar Boot problems in this and other forums.