I'm helping my friend put his pc together its a P4 3ghz prescott, P5P800 mobo, ati 9800 pro, Audigy 2 sound card, 2 sticks of 512 pc3200 DDR 400 crucial ram, Antec 450w power supply, and 120gb Samsung(can't remember specific mobel #). So I put everything together and go to power on. The case lights up, the mobo power led is on, the processor fan runs, all other case fans run, the video card fan is running, yet there is no Post. Nothing comes up on the screen.

I checked all the jumper settings. I had orginally set the jumpers on the HD to master, but changed them back to default which i think is cable select. still no post. Cleared CMOS, no post. Power cycled the PSU, still no post. Tried using a different monitor, no post.

One thing to note is that the exhaust fan on the PSU is NOT working at all.

I took the video card and hard drive home with me to test them, haven't done that yet, but I would think that I would still hear the beeps from Post even if it was a display problem. I installed everything while grounded by an anti-static wrist strap, and i kept all the parts on an anti-static mat on the table so I'm 98% sure I didn't shock the mobo. any ideas? Is it a dead mobo? thanks ahead of time for your comments.

Hi and welcome to PCHF

Firstly for me, the fact that the fan in your PSU doesn't work is ringing alarm bells! Can you test that too...it could be a problem that the power, or the right amount of power isn't getting to where it needs to go to power that nice new PC.

There could be a problem with the mobo but let's get that PSU checked out first

Last time I had this problem I forgot to connect a small cable from my PSU to mainboard. You are sure of connecting al cables (and the right way)?

ok, heres the update. I switched out the PSU from my working pc and put it into my friends, still no post.

I realized after I had disassembled the entire computer that i had not connected the 12v 4pin connector from the PSU to the motherboard.

At that point though, i had already taken the heatsink off and removed the processor.

From what i understand about thermal paste and arctic silver 5 is that once its exposed you have to reapply??? is that correct?
at any rate i re-applied arctic silver 5 and put everything back together plugged in all required power plugs i.e. 24pin connector to mobo, 4pin connector to mobo, and everything else that needed power. Turned it on and still no post. My guess is that the mobo has a dead spot.

However, this time when i connected everything I was using my friends PSU(the one with the non-functioning exhaust fan) and not my PSU which I know works. (I would have used my psu, but I had to drive back to my house to get the arctic silver etc. . . and i took my psu back with me figuring that since i hadn't connected the 12v to the mobo that that was the reason for the lack of post.

side note: I tested my friends video card and hard drive and both worked fine.
The case that my friend has does not appear to have a case speaker, sooo the mobo could be posting and I wouldn't know?

anyway, this is just an update.