Orange light, but computer not turning on.

[sketch22]

every time i try to turn on my computer, i press the power button and an orange light blinks once, but the computer doesn't start. i tried opening the case while turning it on, and when i pressed the power button, all of the fans spun a little, and 2 very small red lights blink once on my GPU. today is the first day that my computer wont start at all after a bunch of tries, and usually my computer will start if i keep pushing the power button. any suggestions?

Dell Studio XPS 435mt
4GB RAM DDR3 (4 sticks, 1GB)
ATI Radeon hd 4850
intel core i7 920 bloomfield

 

[Hoku]

Had the same problem with my XPS 435MT. The power button glowed orange and computer wouldn't start. Checked the PSU and the LED on that was green. However, while the stock Delta PSU is rated at 360W when new, it degrades over time. I replaced the PSU with a 600W modular cable unit that has a big 135mm downward facing fan that blows out the back of the case. Had to bend a tab down on the inside of the case for it to fit. Recommend a modular cabling system PSU as it's a tight fit.