I get this a lot. If you are not sure if your desktop computer is getting power, double check that first. If you are sure your desktop computer is getting power, here is one trick you can try. Unplug the power cord from the back of the computer, while the cord is unplugged, push the power button in 5 times slowly. Next release the power button completely, then plug the cord back in. Finally try turning the computer on again. Does that help? Please let us know.
