Try the old generic reset.
I'll write it for the laptop with the longer version over in the troubleshooting forum so ignore the battery if this is a desktop.
Remove AC POWER, slip out the battery (laptop only) then press and hold the power button for a full minute. Release button, slip in battery, apply AC and try again.
I've got a little problem today with my Inspiron 530. I went to turn on the computer by pressing the power button on the front and nothing happened. I looked at the back of the computer to make sure it was properly plugged in and there was no power light on in the back. I unplugged the machine, reset the surge outlet and plugged the cord back into the computer. The green light on the back near the power cord came on (steady green light) but it still will not power on using the front power button. No fan, no lights in front, nothing. Everything was working properly the day/night before. One issue I did notice a few days ago was while going to turn off the computer I accidentally clicked on "sleep" instead of "shut down". Instead of actually sending the computer into sleep mode the computer powered down. It started up fine a few hours later after shutting itself off. I have been having issues getting the computer to come out of sleep mode in the past month or so. It's past it's warranty and about 3 years old. Any ideas?