Computer won't start, can't be PSU

[renome]

So,today I was playing Alpha Protocol and all of a sudden my PC just shut down. I tried turning it back on,but with no success. When I opened the casing, I could smell something burned, but everything looks fine. 3 weeks ago, I bought a new PSU (500w) and a technician installed it,claiming it's more than powerful enough for my computer. I own Nvidia 250GTS, 2GB RAM and a 3,6 Ghz single-core processor. Strangely, motherboard still shows me the green light for my power supply and when I try to power on my computer a green lamp in front turns on and a red lamp under it briefly flashes. The green lamp in front turns off only after I hold the power key for a few seconds. Oh and, there are no sounds coming from the motherboard or the speakers when I try to power up the PC. Any help would be appreciated.

Edit: If it helps, here's the video:

http://www.youtube.com/watch?feature=youtube_gdata_player&v=K69Gdz0LrkU

 

[Tmagic650]

It IS most likely the power supply. Just because you have a couple of green leds, doesn't mean that the power supply is good. It could me the motherboard, but try a new power supply first

 

[renome]

What's bothering me is the fact that the power supply is brand new (3 weeks) and that computer wasn't used a lot since it was installed, so how can a perfectly good and new piece of hardware just die?

 

[Tmagic650]

Power supplies are way cheaper and easier to replace than a motherboard. Any piece of electrical equipment can fail at any time

 

[renome]

Huh, looks like I'll just have to try exchanging it with a warranty, thanks for the help. Just out of curiosity, motherboard and PSU are the only 2 possible theories?

 

[Tmagic650]

As I said, the power supply is the easiest part to change. Sure it could be some other component, but in my experience, the power supply is bad