computer down, Asus motherboard 5b_pwrd led on

I left my computer on the whole night, in the morning when i woke up it was turned off (no sleep or any other strange settings configured, i always leave it turned on for days), when i tried to turn it ot it wouldt even start

no noise, nothing at all

the only thing i noticed was a greend fixed led light on my mother board turned on all the time, my motherboard is an asus p8h67 and the light has a tag below, named '5b_pwr'

what can be goin wrong? the motherboard or the supply?
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>but since the motherboard is getting power from it i assummed it was working fine ?

No, it can turn on, but not deliver enough current to boot the system.  Do any of the case fans or hard drives spin up initially?  Power problems can be the due to the power supply or the motherboard, since the power needs to be regulated and divided among the components on the motherboard.  Try to get a replacement power supply to try.
Remove the power cable, and then also the CMOS battery. After that return the battery again and plug the mains cable back into the powersupply and try turning the PC back on.

If the PC boots now, turn it back off and clean out all dust, make sure the fans run smoothly, remove the heatsink from the CPU, and then clean it's and the CPU's surface from any thermal paste or pads (industrial alcohol is good for that). Then apply a very small drop of fresh thermal transfer paste to the top of the CPU and firmly reattach the heatsink. PC's turning off are often caused by overheating, and the above makes sure that shouldn't be an issue for some time.

A further cause are bad electrolytic capacitors, so check their state (look for cracking, bulgin or leaking signs on them). Those caps can also be inside the PSU and on the Graphical card.
celticianAuthor Commented:
Ive just followed all the steps and the pc is not turning on :(
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Do the caps still look fine? Have you tried another PSU? Also make a "barebone" of your PC (remove everything you can so it only has the minimum, no external devices, no HD, Floppy Drive, CD Drive, Keyboard, Mouse, Printer, expansion cards attached), only one RAM module. Just leave the display connected. Then try turning it on again. If it displays something, turn it off again and one by one connect things you removed and try starting it again, until you find what is stopping it from booting.
celticianAuthor Commented:
I dont have another PSU, but since the motherboard is getting power from it i assummed it was working fine ? im trying to remove all the other devices but the board to see what happens...
Even if It gets power, it may not be enough or it isn't stable. Also, a PSU outputs different voltages. Maybe one of those voltages isn't there.
Scott CSenior Systems EnginerCommented:
Do you have a friend who would be willing to loan you a power supply to test with?  

I'd say it's a 45% chance it's the motherboard, 45% it's the power supply and 10% it could be a card or optical drive.

I've had fried modems and bad optical drives keep a PC from booting.

To keep it cheap, do you have any local flea markets close by?  You might be able to pick up a power supply for around $10 to test with.  That way if it's not the PSU you are only out $10 but you will have a spare one for future use.

If you do find one at a flea market, make sure it has enough power and connectors for your your system.
Is it an emachine?
nobusbiljart fanCommented:
the first step would be to test with a known good PS - borrow  one from a friend, or have yours tested in a PC shop
you can also use the minimum setup as described in this guide to troubleshoot (less  devices = less power needed)                  (Short-overview-of-how-to-troubleshoot-bad-hardware-when-a-pc-does-not-post)

in case the disk has problems,  - use this guide :
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