Thanks to all who posted this fix. I just had the exact same symptoms from a Dell 620. I couldn't get the computer to not power on. The customer would take it home, plug everything in, get it to turn on once, and then after that it would not come on again. They brought it back to me for repair and I couldn't get it to fail to power on. They took it home and same problem again. After reading this thread the light bulb came on. I asked my customer if she plugged anything into the front usb ports. She said she had always plugged her keyboard in the front. In all my testing I had always plugged the keyboard into the back usb port. So I had here move the keyboard to a back usb port. Guess what, it powered on without a problem. She'll let me know if it stops coming on but not having anything plugged into the front usb ports when powering on the 620 seems to be the answer. Don't know what the fault is in the Dell motherboard for the front usb ports (or the port itself) but maybe there is some kind of a 5Vdc fault or overload condition that the crowbar circuit in the power supply is detecting and prevents it from powering on.
After purchasing a new Dell power supply and installing, nothing happened. Read this information and cannot believe that after disconnecting two of the USB cables the computer powered on... so frustrating! Our 620 Desktop has been so reliable until our last power outage. Just figured it was time for a new power supply.
Dell needs to find out what is causing this and posting on this site so we can repair them. I just kept the cables disconnected for now. Thanks to all those that figured this out or we may have just bought a new computer.
UPDATE - the original bug (failure to power on) returned with a vengeance ! A replacement power button cable assy was purchased long ago and seemed to fix the bug but for some unknown reason recently failed. The original cable assy that came with the machine was re-installed but it too failed. Since there is a spring-loaded button which, when pressed, starts the power on sequence it seemed reasonable that both switches (original and replacement) were defective. The switch was removed from one cable assy and the 2 leads were "shorted" together - power on started but quit after only 1 second ("one small step for man"). However by "un-shorting" the 2 leads and just touching them together briefly the power usually turns on. But on one trial a USB device had to be removed from a REAR port before the machine started. Apparently the tech gremlins have taken control of this <profanity> from Dell. They used to make sturdy equipment but apparently have decided to focus on profits by using cheap components and refusing to make needed upgrades for their faulty machines.
I bought an Inspiron 620 slim back in September 2011 and has worked great until today. I had the same problem as reported in this forum.
So I just unplugged the front panel USB connector (USBF1), the one that has a green plug on the end of it, and the PC started. I then turned it off, plug the cable back in and it started again. I then tested the front USB ports and memory card reader and everything worked.
I'm hoping this will not happen again, but if it does, I can live without the front USB ports.
Hope this helps.
Thanks to all who posted before regarding this problem.
My 2 cents: Removed front usbf2 from motherboard and restarted computer with no problems. What gives, Dell?
Yay! Worked for me. Just unplugged all 3 connectors and left them unplugged. Didn't start with the first button push but did with the successive frantic pushes. Guess I'll have to get a new desktop because Dell hasn't come up with a cure. I can't trust this one now. I did notice over the year or so I've been having trouble with this problem that if I select restart it starts every time but if I select shut down most of the time it won't start unless I unplug all the back panel plugs and wait a couple hours. This time that didn't work but unplugging the front panel plugs did. Thanks.
My house power went out for a while last night. Now my Dell won't start. I guess unplugging those plugs was only a temporary fix. Now what?
Hi Mineo: apparently dull (Dell) tech support is still sleeping since this has been a known bug for MANY YEARS.
I now own FOUR power cable assemblies (reasonably priced if NOT bought from Dell) - one works consistently if only 2 USB devices are attached to REAR ports during power on. Be sure that all 5 cables from FRONT panel to motherboard are disconnected (at MB end). There are only 3 connectors on my MB for 5 cables (thanx Dell).
Good luck !!
Thanks Arbee3. I got a pm from someone at Dell. They checked my warranty status and hinted it might be the motherboard. So since it's out of warranty I decided to take out the hard drive and put it in a case. Now I'm using it as an external HD.
If I ever hear the solution maybe then I'll try to get it up and running again. Until then my pc sits idle.