Out of the blue, pc wont boot...

Hola..
Pc wont boot, motherboard led comes on, keyboard lights flash, fan starts, can hear HDs start spinning, but nothing on screen, not even BIOS, nothing. Buddy of mine lent me graphics card that he swears works right, which I put in temp to check whether mine was to blame maybe; not that either, still nothing on screen. By the way, I did hook up my monitor to my laptop and it came right up, so it's not the monitor either. I even checked voltage with a multimeter coming from the power source (400W), and the yellow is consistently at 11.88V (somewhat below the supposed 12V) and the red is at 5.21V (somewhat above 5V). These values hold even if I disco the HDs and the CD drive before I boot. I measured the 20 pin motherboard power-connector values also and they are all within .4V of their specifications. I don't think this is a power issue. I also visually inspected the CPU (did NOT pull it out), seems ok, no reason to believe any pins broken, never touched it since install, no major trauma or kicking occured; I only do that to my cat when something dont work (just kidding ). So I assume it's gotta be the motherboard, though I cannot imagine what could've gone wrong. It's and ASUS peice: P4T533-C. Took all 4 memory sticks out, without which motherboard dont work, I know this from when I put it together, and put them back, making sure all is clean and secure. Any ideas, suggestions on what to do next would be greatly appreciated!!! I REALLY dont wanna take the board out, takes too long..

Doesn't sound like a power issue to me. Is your buddy sure that the graphics card works ? I still think that is your problem as it definitely can't be the monitor when that works fine when connected to the laptop.

If you leave the machine, do the fans continue to spin, hd continue to make noise like it's booting etc ?

If you leave the pc on for a couple of minutes does the hd led start blinging like its loading? I doesn't sound like the motherboard is bad, sounds like graphics card

Have you tried the following:

1. Boot mobo with only Proc, HD, memory and video.
2. Boot mobo with only 1 stick of RAM. Try all four sticks you own seperately?
3. Reset the CMOS jumper? All ASUS mobo's have a CMOS jumper that you can mess with to restore factory defaults to your mobo. Check the ASUS website for your model.

Did you mess with overclocking at all? What kind of memory are you using? Did you properly configure the timings prior to this problem?

I had an ASUS mobo that got completely screwed when I pushed the memory timings past their limits. I was using average, CAS3 RAM. Once I pushed it too far, it wouldn't boot again, no matter what I did. The only way I could fix it was to boot using CAS2 RAM so that it could handle the timings I had setup.

Hope this helps!