New system won't power up

[Ecwfrk]

I just finished setting up my new comp and it won't power up. When I turn on the power the fans spin up for a fraction of a second and then the machine immediatly shuts down without any fault codes. I've checked the power supply by itself by jumpering the power connector and it stays on. But when I plug it into the Mobo it always does the same thing.
I've tried unhooking the power connectors from everything with the same result. I'm about to pull the ram to make sure that's OK. I've already checked out the processor and it's fine.

Any ideas what's causing the power up problems?

 

[mechBgon]

You haven't mentioned what hardware you've got, so this is just a guess: you've got an AMD-based system and you put your heatsink on backwards. The CPU overheats as a result and shuts down (yes, it really can overheat in one second ). Take off your heatsink and look at the base... it's got a step cut into it, like so: photo of heatsink bottom That end of the heatsink must match the raised, solid-plastic end of the CPU socket.

If your heatsink came disassembled, also make sure you've got the clip into it in the correct direction... when the heatsink's on correctly, the pressure point of the clip should be centered over the CPU core (it's asymmetrical).

I hope I guessed right and was of some help. If this isn't the issue, the next-most-likely one is that your motherboard is expecting an RPM signal on the CPU-fan header and isn't getting one (read the manual carefully, there is usually a way to override, such as holding the Insert key on SOYO boards).

 

[kurtaotto]

I had a similar problem a while ago when I ungraded my cpu cooler to a Zalman Flower with speed controller. My problem was that the bios was detecting a fan faluire do to low speed I believe. If your cooler has temp control or other form of control for the fan then if you can set the fan to spin a max speed. This should allow you to get the computer running. If you don't want to run the fan a full speed (due to noise most likely) enter the bios and go to the pc health section if it has one. There should be a setting to shutdown the pc in case of fan failure. Disable it or inspect other settings that may be causing the problem. You should be able to run the fan at what ever speed you want after that.

If the above doesn't apply to you, do you have a strong enough power supply? If your running an Athlon XP you'll need at least 300W as recommended by AMD. Let me know if any of this helps.

 

[BarryAZ]

We need more detail as to the actual power supply, motherboard and CPU combination.

At a guess, either the CPU Fan is not quite doing its job, or the motherboard is not detecting the fan working, or the power supply isn't up to the task.

For what it's worth, my own start point for either P4 or AMD XP CPU's is 400W. I relegate my 350 and 300W ATX power supplies for Pentium III systems.