Yes, a yellow light indicates an internal power problem or device malfunction. Try reseating your ram modules, check the power connections, and reseat the cpu, video card, and expansion cards. If you have another computer, you should try switching around all the compatible parts to see what is broken.
What you were doing before the PC failed in this case is mute. If you had been burning a dvd or editing photo's before you shut down the PC you would be blaming it on that I suppose. If a PC is about to fail then it will fail no matter what you were doing beforehand. Follow the suggestions you were given, if you have a Dell compatible powersupply you can swap with, try that.