Is the power button LED, solid green, blinking green, solid amber, blinking amber?
What is the reading of the diagnostic LEDs on the back panel? <ADMIN NOTE: Broken link has been removed from this post by Dell>
Unplug the cord from the power supply, hold the power button in for about 15/20 seconds, open the case, unplug the 24-pin connector from the motherboard and jump the Green wire to one of the Black wires, reconnect the power cord and if power supply fan and hard drive runs, then the PSU should be good.
Note= Do not remove any wires from the plug, use a small piece of wire or a paper clip as a jumper.
Please don't send me questions about your system by DCF Messenger.
Post the issue in the appropriate Board, where they will be answered.