No power except fan

Unplug everything inside the computer, except the motherboard and the front panel power on switch. Power up the computer. If the PS fan continues to run, (power supply doesn't shut down)and the CPU fan runs, then power off the unit and reinstall each device, one at a time, turn the power supply on after each device is installed (and off, before installing the next device).
You can not easily start the power supply if it is not connected to the cpu motherboard.
If the power supply shuts down with only the motherboard attached, then you will need either another power supply, to test the MB, or another MB to test the power supply.
R

Does it show the hard drive in the bio's? If so and you have the operating disk,,, load the drivers from the disk and when prompted, use the repair mode provided therein to check disk (CHKDSK) It will scan and repair any defects that may be causing the program to not load.

Indicates a power supply failure, needs a few filters replaced expect to pay $100-150 Julio [email protected]

check if there is a switch on the back of your power supply if there is try turning off then on again .still no power replace you power supply

ok dandan, please tell me you live in nj. I am having the same problem with my puter and did every step you did what is up with this??

2 questions:
When you say new motherboard do you mean an actual new motherboard or new to that machine, but came from another used model?
When you say you tested the power supply do you mean with a voltmeter/ammeter or put it in another computer and it worked?
I worked on several gateways with similar problems and it boiled down to motherboard issues.
I tested it by replacing the power supply with a bigger (used) power supply and it worked great (for 1 time) and then put the other power supply back in to confirm my diagnosis and yep it wouldn't boot. The next morning I was going to run some virus/malware cleanup and installed the other (known good) power supply and it would not work. I tried all day to get it to boot and it did about twice in a 4 hour period. When it did run it would run great but any attempt to restart it would cause it to crash. No ryhme or reason, it would not fail the same way more than twice. Sometimes beeps, other times no beeps, sometimes it would start up with no video (could hear the Windows starting sounds) other times it would start up normal. I could let it sit and it would start or I could keep trying in sucession and it would eventually start. Some times the fans would slow down from a roar, sometimes they wouldn't. So with a known good power supply that had 150 more watts than the original I diagnosed it as a failed motherboard. But if you have put in a brand new motherboard then I would replace the power supply, because a bad power supply does not mean no power, just not enough power. Please post back and let us know what you find out.

Check the switch of the power supply at the back (black button) First
If the power supply fan doesn't work or cpu fan doesn't work
Replace the power supply.

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Try you system with a known working power supply. Your power supply could have an intermittent problem. It could be a lose wire or a capacitor problem. Putting back your system, Plug the 20 pin/24 pin power connector to the motherboard, plug the 4 pin extra CPU power in place, plug the panel connectors(Power button, reset button, LED...).

Check all power cables plugged into M/board if these are correct
remove all hard ware
hard drives / cd player and anything else
except for video and memory and test to see if it boots. If it does, one of the removed hardware is faulty if it does not then you have M/board failure

power supply is probably shot and you are feeding a voltage way over what is needed. I have a dell that refused to operate one day. I went to www dot affordablesurplus dot com and found a 350 watt power supply with all the RIGHT plugs. Never had a problem since.