Computer Suddenly Wont Turn On! Please Help!

I fell asleep watching some Netflix on my PC as I always do and it generally goes to sleep when what I say went watching is done and when I hit the mouse or keyboard it comes right back. Simple. Today when I woke up it was still on
was on, fans running, lights on and all that but when I tried to wake it up it wouldn't show or do anything on the screen. So I went ahead and powered it off by holding down the power button and it turned off. Then when I tried to reboot the computer won't do anything at all.

I unplugged the power cord and waited a few minutes and then plugged it back in and tried again but no change. Nothing. I looked at the inside and saw on the motherboard (Asus P7P55D-E Pro) the Standby Power LED was on and green but I am stuck what to try next. I unplugged my USB dongles, external hard drive, audio cables but no change.

I am stuck what to try next. It just seems very strange that while it didn't respond the computer was on and then poof! Nothing. With the standby on, it seems like it should at least post something, anything.

So... Any suggestions? Please please please. And thank you in advance.



Addition (Possibly important): My external hard drive is powered separately but when I plug it in to one of the USB ports the drive will begin to spin up.



Addition: Besides the green standby light the DRAM voltage switch will come on red when switched.

 

Check the monitor.

 

So no fans going? Does the power supply fan spin? When you unplugged it, hit the power button, then plug it back in and hit the power again.
I'd get a power supply tester or another suppply and test that.