Dell Dimension E520 Flashing Yellow Lights

[Ramasoma]

Hi Everyone,
I have a Dell Dimension E520, that recently stopped working. For the last month, I have needed to click the power button multipled times to turn on my computer. I have pressed it, the light turns yellow for a few seconds and shuts down. This was happening constantly for the last month, and it took me 5 or 6 tries to turn on my computer and keep it on. Finally, today it would'nt turn on. I tried clearing the CMOS and what was wierd was that it went from not turning on to a flashing yellow light. Also, I tried doing the paperclip test with my power supply and the fan spun, but it made a wierd continuous noise. What do you think is the problem? I removed all the components except the power supply, heat sink for processor, and motherboard. What do I replace? Any help is greatly appreciated.
Thanks,
Rama

 

[Ramasoma]

Some other information, I took out the battery from my motherboard and plugged in the power and found that a yellow light on the motherboard began shining. Does this mean that the power supply is giving energy to the motherboard? Also, when I plug in the power, the fan spins for a second and then stops. What does this mean? What do I replace? Thanks for any help!