Dell Vostro 400 will not power on
If you are having an issue with your Dell Vostro 400 powering up, here is something that worked for me.
This morning our Dell Vostro 400 would not power on. The light on the power button was yellow in color. I took the side off the case and noticed that when the power button was pushed, the cpu fan briefly spun and stopped (this usually indicates an issue with hardware in the computer). I went ahead an unplugged the power from the computer and was going to proceed with removing cards and memory. I removed the graphic card and plugged the computer back in. When I turned it on, the computer started to run, thus indicating that the graphic card was the culprit. I simply replaced it with a spare and the computer has been working flawlessly.
If the graphic card was not the issue, I would disconnect the hard drive and then the memory (1 at a time with trying to power up the computer).
Hope this helps someone out.