HP Pavilion won't power up.

Well today i tried to turn on my hp pavillion a1440n and it wouldn't turn on. NOTHING happens when i press the power button. The fans don't spin teh power button doesnt liht up, nothin. There is absolutely no sign of life. The only remote sign of life is that the tiny green light on teh back of the power supply is glowing. i tried a different outlet that i knew was working and still no luk. I also tried to drain teh power by unplugging it and holding the power button and still no luck. It was working fine last night. I'm thinking it's a PSU problem? an anyone confirm for me? The entire computer is stock except for an additional 1 gig of ram i added and the nvidia geforce 9500gt graphics card i added about 4 months ago. Thank you.