Help! It worked for 2 days and now it wont turn on!

[mcgrym]

So for the first time ever I built my own rig. After a few hours tolling over it and reading through the motherboard manuals I got the thing to turn on, used it for 2 days without problem it ran
perfectly fine without any hitches. So this morning I went to turn it on and the power led lit for just a milisecond and that was all that happened. I checked to make sure everything was still hooked
up and nothing had accidently come unplugged. I even thought maybe I was trying to pull too much power from my powersupply so I unplugged a few fans (not the CPU fan of course) and took out the
graphics card still no response when I hit the power button. I would really appreciate any help advice or things I can do to narrow down what the problem may be. I plan on taking it to a computer
repair shop to get a diagnostic.
what Im working with:

Diablotek Epic atx mid tower case
Diablotek 450 Watt atx powersupply
msi 785gtm-e45 motherboard
Amd Phenom 2 quad core 2.8 ghz processor
The CPU fan in it is an ultra 12w xwind /heatsink combo.
The case has 2 fans on the top one in the front and one in the back
I doubt whoever is going to try to help me will really need all this random info but I figured I'd put it in just in case. I am running XP on it or was until it decided not to turn on for me I also
did try it in different outlets with no luck and I even tried my old 250 Watt psu on it just to see if there was something wrong with the power supply. Sorry if this post is grammatically whacky or
spelled strange in places I was forced to type it from my phone haha if anyone thinks they could assist me with my issue feel free to drop your 2 cents please keep in mind I am new to the build your
own rig scene so it could be a simple or stupid mistake I've made.
PLEASE HELP ME!

[orbrit]

Start with this procedure
PROBLEMS with a NEW BUILD? Try This!!

Essentially you want to try and eliminate something.
Sounds like you already did that with the PSU.

But start with the basics - make sure both motherboard connectors are plugged in (24 pin and 4 pin CPU)
Single DIMM of memory
No add in video - just use the onboard

[glc]

PROBLEMS with a NEW BUILD? Try This!!

Take the motherboard out of the case.

Please don't take offense, but Diablotek power supplies are poor quality. It may have popped and took the motherboard out with it. MSI motherboards aren't noted for reliability either.

[Nikon]

im curious as to what videocard you had in it.