Question Computer suddenly wont boot up after restart. Help Please

[Dougyyyyy]

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.

 

[Steltek]

First of all, firmly reseat all your memory modules and both the ATX 24 pin and EPS 8 pin power connectors on the motherboard. Unplug the USB hard drive cable. Do any of the fans (CPU or case) spin when you turn on the computer? Does it make any beeping sounds through the speaker when you turn it on?

Try unplugging the power and SATA cables from your boot hard drive as well and try to power the system up. Does the system respond in any way?

What make and model of power supply and video card do you have? Has the system ever been overclocked?

From section 2.9 of your product manual on page 2-41, are any of the POST LEDs lit (DRAM LED, CPU LED, VGA LED, or BOOT DEVICE LED)?

 

[VirtualLarry]

I had something similar happen to me a long time ago, somehow, the PC got put into sleep mode, and then power got cut, and I had a dickens of a time trying to get it to boot into normal mode again. I don't remember, but I may have had to use the CLR_CMOS jumper.

Then again, sometimes if the mobo or PSU goes KAPUT, the system can appear to boot in SLEEP MODE too.