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A powercut killed my computer!

Fire Boar
This morning, there was a five-second powercut in my house. It reset all the clocks, but nothing too drastic happened: it was merely an annoyance. That was until I tried to turn on my PC just now. Nothing happened. The whole thing had gone caput.

On investigating further, I discovered that there was power going to the computer, as it was making a tiny little "buzz" noise (very faint, but definitely there). On looking inside the computer I discovered that it was being made by a green LED, just on the edge of the motherboard. I am unsure as to whether that LED would have been on if the computer was working. Anyway, I think it might be a problem with the connection from the power supply to somewhere. I'm not all that good with the ins and outs of a computer, so any advice would be great.

I assume that the pc is not booting up.
Check your motherboard's owners manual that should have came with it.
The green LED is probably supposed to be on.

Do you get a any beeps at all when you try to boot/reboot it?

While you have the cover off, blow all the dust out of it.

Unplug and reconnect/reseat all power supply connectors.

Power transients are very hard on power supplies.
If you do not get any beeps at all, that's a bad thing.
You could get a power supply tester at Circuit City for ~$18.
Or, swap it out with a known good one.
this very thing has happened to me before.
It's probably a problem with the power supply. I would replace it, since these things aren't very expensive.
Fire Boar
Well, I came up to have another go at sorting out the computer and it suddenly started working. Before, it wasn't booting up at all, the power light wasn't coming on, the fan wasn't coming on, it just stayed as if I had not pressed the on button. But when I tried later on, it worked just fine. Weird...

Anyway, I've got rid of as much dust as possible, and it's working without a hitch now.
I've seen this before. First everyone should have a UPS. You don't need it for the battery backup totally. A UPS will protect your PC during brownouts, no power and power surges. Power strips are crap and almost never help.

As for having no power to boot your PC, you can get it to boot right off the bat. Remove the power plug. If there is a voltage switch on the power supply, flip this, then flip it back. Basically you want to reset the power supply. Plug it back in and it should fire up right away.
Fire Boar
@flameboy: I'm not stupid, that was the first thing I did. Guess what, nothing happened. The green LED suggests that power is getting to the computer, so it's hard to believe it's the power supply. And anyway, I'm not a millionaire, I can't afford a UPS. My surge-proof power adapter does me fine.

Computer's back down now. It's quite infuriating actually. I'm hoping it will go back up, but if not I'm getting someone in with a power checker thingy, to see what isn't getting power. In the mean time... I'll just keep fiddling.
It looks like your PSU is the cause of the irregular behaviour of your computer. Had one unit in the office acting like your PC until i had the PSU changed. Try giving a few light taps on the casing close to the PSU and see if the PC turns back on. If it does, then it's a faulty PSU and it's time for a change.
Fire Boar
You're absolutely right. The voltmeter I bought says that there are 4 volts coming out of the PSU instead of 5. So the mobo was getting power, but not enough to turn the computer on. I looked it up and found that the Antec power supplies aren't all that reliable, and other people with ASUS mobos had been having similar problems after 6-18 months of normal use (my PC has an age of about 12 months). So I've got a new PSU, one that's really reliable, and it's working perfectly. Thanks guys.
Buying a good psu is very important for the heath of the computer.
The problem with your PSU, was probably that the capacitors(i am not sure that this is how they are called in English) were overpowered, and thats the reason why your computer couldn't start. After some time, the extra power slowly faded away, and that is the reason that it miraculusly started to function again.
Next time, unplug the power supply, and press the power button a few times, extendently, that would help uncharge the capacitors quicker.
If you experienced a power outage very briefly, it may have very well blown out your power supply. If it was connected into a really cheap end surge protector, then it STILL is possible to blown our your computers power supply. A surge protector shuts everything off within the blink of an eye, everything is shut off in a hard way. If you would like, you can look into getting a MONSTER surge protector, they have them for computer, for rougly around $40-$50, they can be pricy, but they cover you very well. If a power outage occurs, the surge protector does not act like one of those $5 ones. Instead it softly shuts everything off without any harm.
One of my old pcs got damaged by a power surge so i have all my electrical stuff on a surge preventor gang nowadays.

Havn't had a problem since then.
It is more than likely that the PSU has been damaged as this is obviosly the first thing in line from the mains cable, Although you have a green LED lit on your motherboard it does not necessarily mean that the PSU is working properly as it is multi-tapped ie. it has 0v +5v +12v etc etc... so for example you may have the +5v and 0v but not the +12v. You can buy PSU testers pretty cheaply:-

But you maybe better off just replacing the PSU as they are not very expensive. It is also possible that a surge could damage the motherboard, but in my experience USUALLY the PSU absorbs the damage first.

Hope you get it sorted out

yeah like all the others said it is probably the Power supply.
Might i suggest this one:
its $39.99 and has more than enough connectors
Power Provided
350 Watts

Drive/Power Connectors
(4) Molex 4-pin Connectors; (1) Floppy 4-pin Connector; (1) Serial ATA Connector

Motherboard Power Connectors
(1) ATX 20+4-pin Motherboard Connector; (1) +12V 4-pin Motherboard Connector

Power Supply Cooling Fans
80mm Ball Bearing Fan
check your SMPS, if it is ok.. change your bios jumper settings, this may solve your problem.
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