Honestly, my experience, that is generally how it happens. In truth, it could be much worse. You could have lost your hard drive. Failed motherboards are a headache to replace, but at least you didn't lose any data.

Oh, and the suggestion to get a UPS is an excellent one. I lost 2 hard drives due to power failures/surges within a 3 month period. I've been using a UPS since and haven't had a hardware failure since (other than a faulty optical drive). A UPS will save you more headaches than you can possibly imagine.

BTW, you mentioned your computer was a self build that was only "months" old. I'm going to assume your motherboard is still under warranty. You should get an RMA. That is, depending on the motherboard. If you didn't get a premium board, I might also recommend upgrading it while you're at it. There's almost nothing more important in a system than the motherboard.

Quoting the most relevant information. If you are not even making it to POST, it is most certainly not a problem with a hard drives, keyboards, graphic cards, or most other peripherals. Failing to POST is a failure of the most basic functioning your computer is capable of, which strongly indicates a motherboard failure. I believe you would also fail POST in the event of catastrophic CPU failure, but I would lean towards motherboard failure, simply because it's more common.

The power supply, of course, is also suspect, as without regular, consistent power all sorts of things will go wrong. However, power supplies rarely fail gracefully - they're either on, or they're dead.

EDITING just to reinforce what others have said - get a UPS. A small one will do wonders for your networking equipment's reliability, and a decent size, good UPS for your computer is the best investment you can make for protecting all of your sensitive, likely expensive, computer parts. Consider it a $150-$200 insurance policy on a $1000+ gaming rig that has the added feature of keeping things running when the power goes out.

If you have a spare PSU, I would try swapping that in first. It's less hassle than replacing the motherboard. Otherwise, remove any discrete cards, reseat the memory and disconnect & reconnect the PSU cables.

My first motherboard was DoA, but my second blew without warning. It also took out the CPU and GPU with it, or the people of the computer store managed to break them while dismantling the PC. Now that sucked some serious ass. Warranties covered everything, but still.

If the fans are still spinning, I strongly suspect the motherboard.

As uscere already said, PSUs usually die a very thorough death. I've had several die on me, either shorting out the power in my entire room when switching on the computer, or simply failing to provide any power at all. Never had a partial failure, however.

if u have a spare - try changing the battery on the motherboard.

No, it probably is. If he has an extra it's worth trying to swap it in though.

I've seen a partial failures and the symptoms match as does a faulty motherboard.

When this happened to me it ended up being a memory problem (possibly a faulty socket though, so still possibly the motherboard). I didn't have to get a new motherboard. A faulty motherboard appears to be the most common cause of this problem though according to this thread and other places I looked.

The lesser known power supplies like to take out motherboards as well. I had a lesser quality name brand power supply take out my motherboard when it died (quite a few years ago).
Also, if it's a recently built system (last three or four years), you can boot without a keyboard attached. Motherboard manufacturers did away with that little error sometime around when USB keyboards started to enter existence.
Last one I saw in the intel world was the Pentium 4 days that required a keyboard.

Sounds suspiciously like a motherboard failure, to me.

Not to mention hard drives, etc.

I had one that started smoking, literally. It was powered off before there was any flames. ;) Surprisingly, the motherboard survived that one.

Given that it's a self-built computer it's entirely likely that there's just a loose connection in there. I had that once. Scared the shit out of me. But easily resolved by double checking everything in there.

That would have been awful. Back in the floppy days, I blindly hooked up the power either backwards or off by a pin and the same thing happened (smoke on boot up). The motherboard, floppy drive, and power supply were actually fine afterward, but I had to air out the room.

give newegg or amazon a call and they'll send a replacement board, easy peasy

all of the main reasons have been mentioned, id second the bit by bit step.
however i have had a pc react like that twice, for two different reasons - one the room is too cold (seriously! it was causing the metal to contract and parts / cables were not making a connection - you can guess how long it too to try figure that out - why after it was fine hours later when I left it on and got called away!)
and iv had random error messages indicating a mobo failure from a DVI cable being placed in the second input on the gfx card.
some times i get the most bizarre issues and given the opposite of what it SHOULD be. but yeah ignoring my bizaro incidents above, id go with mobo issues. but also could be your PSU is having too much power drawn from it and resulting in issues or psu is about to die.

ive had one rig where i just couldnt figure out why it wouldnt boot, - no error message or anything just would boot and sit there. turns out for some weird reason the PSU just didn't like the Mobo, even had all parts independently tested and they were all fine, even in more power hungry systems etc. but as soon as you put that psu and that mobo together nothing.
Thinking about it i get the most odd issues either for myself or for people who ask me to help!