To clarify an earlier post, my dell dimension 4600 tries to turn itself on when the computer is off. It blinks on and off several times untl I hit the power button, then it boots. Other times when the computer is off, I cannot turn the computer on by using the power button and I need to wait until the computer blinks on and off. I need help and I am getting nowhere with dell. Please!!

Hi, I suspect you are only putting the machine into suspend / hibernate and not switching it off. Go into the Dell BIOS and change the power management settings. Also check for Power on LAN settings which could start your computer on a modem receiving an incoming call or network card being ping'd etc. Disable all these settings. Check the power management settings for the condition the computer should return to on restoration of power. If you have a surge protector and turn this on & off, the computer may try and switch on on its own due to this setting. Set all these to always off. hth Ceri

I am having the exact same problem on my Dell 4600. When I shut down (either hibernate, suspend or power down) it attemps a constant reboot on off cycle. I had to pull the plug to get it to stop so it would not do it all night. After restoring power, it will not boot at all. No fans, noises or anything. I do have the green led on the mobo. Would like to test power supply but have no info on it for test points. Anybody have any more ideas?

Ceri, Thanks for the tips, I will check these power management settings. I will also check on if the computer is in suspend / hibernate, but I am reasonably sure I am turning the computer completely off. I have even disconnected the power for some time and reconnected the power. I originally thought it was a sensor on the motherboard or a power setting. Any more ideas would be welcome.

Found power supply to be bad. Had to replace it.