2 Windows 7 PCs suddenly no longer boot, no POST
I've got 5 PCs here.. 2x Win 7 x64 v7100, 1x Vista x32, 2x XP Pro x32. Strangely, within the past 24 hours both of my Windows 7 PCs have stopped booting. They turn on, hard drives spin, fans come on. There is no beep, and no signal to the peripherals, including keyboard, mouse, monitor. Identical problems on both systems.
Specs on Win7 System 1 (2 years old):
Motherboard Asus P5N32-E SLI
CPU Intel Core 2 Extreme QX6850 Quad-Core 3.0GHz
Ram 4 x OCZ DDR2-800 Reaper 2048MB
Video Card 2 x Asus GeForce 8800 Ultra 768MB
Power Supply Silverstone ST1000 1000W
Specs on Win7 System 2 (1 month old):
Motherboard Asus P5Q-EM
CPU Intel Core 2 Quad Q9650 Quad-Core 3.0GHz 95W
Ram 4 x Kingston ValueRAM DDR2-800 2048MB
Video Card Asus GeForce 9600GT 512MB Silent
Power Supply Corsair VX 450W Power Supply
I suppose it's possible that both motherboards just coincidentally failed in the same day but that seems pretty unlikely. They are both ASUS. Has anyone else with an ASUS board experienced similar problems after any recent Windows 7 updates?
On System 2, the second system to fail, I did notice that the computer had been on with the screen saver up for a little while. Someone had been using it only about 20 minutes earlier. I thought it'd entered power saving mode and turned off the screen but when I went to bring it back up, I couldn't. I noticed that the light on the front of the box was flashing. I tried powering off by holding down the power button, then powering back up but had no luck. I also tried turning it off at the power supply and unplugging it for a few minutes but that didn't help either.
Does anyone have any ideas of how I might go about troubleshooting/fixing this? I'm not sure what to do if I can't even get the POST.
Any help would be greatly appreciated. Thanks in advance!