Hi, I just bought ga-p35c-ds3r motherboard and for some reason the cpu fan doesn't work. I have tried with Zalman cnps9700  led fan and the one that came with the prosessor. I'm not getting any kind of signal or post or beep from it either, video cards fan starts just fine and so does my HD's. Everything else powers up except cpu(?) and cpu fan. I have checked that all the connections are fine, several times.  
 
Do I need new motherboard or PSU or do I need both?
 
List of my components:
 
ga-p35c-ds3r
eVGA 8800 gts 320mb
Intel E6750
2x 1gb A-Data Vitesta 800MHz ddr2
450w PSU (came with Antec sonata II)

Try a proper quality 450 - 500W PSU.
 
       Mike.

Antec PSU's come with Antec cases. I wouldn't consider that to be an issue.

cpu fan comes on when it gets warm enough to need it, not sure on the activation temp though.  Don't worry, its normal.  You can watch the heat rise and rpm increase in bios as well.

NO! This is completely wrong.  If the CPU fan doesn't come on at boot time, the CPU can be damaged.

Correction: apparently this is not true for at least certain Gigabyte boards (see below).

I think mike99 is right.  The (smartpower?) 450w that comes with the Sonata II is nowhere enough to power a high-end video card like an 8800 gts.  It only provides at most 15A of +12V for the non-CPU parts of the system (+12V1).
However, it does seem strange that the CPU fan is not turning.  Where exactly are you plugging in the CPU fan (the stock Intel one)?  If it's plugged into the CPU FAN header properly (it should only fit one way), then I'd go with a decent new PS and work from there.  This Mushkin is a reasonably-priced supply that should handle your graphics card: http://www.newegg.com/Product/Prod [...] 6817812002
 

No that is a wrong statement. The CPU doesn't get hot enough to require a fan at power-on.

All Gigabyte GAXXX motherboards have a smart fan control which does not turn on the CPU fan at bootup, but later as the system starts. If you have Fan warnings turn on, you will hear a beep as well.

No, it is not wrong.  The antec case has great air flow.  On start-up, the cpu is ice-cold, that is why the fan does not come on.  I have a friend with the same board, and the cpu fan turns on when it gets warm-enough to need it.  Which, by the way, is probably not needed.  The Zalman 9700 with that case would probably suffice on passive cooling @ stock speeds.    However, the LED should be on.   If it isn't could be a problem with the cooler, or the MB.  Doubt it is the P.S. (although it is pretty week).

Thanks CompTIA_Rep for backing me up.  

OK, thanks for the correction on the CPU fan!

You can use the Gigabyte utility to set a minimum fan RPM so the fan will always be on.
Not having a HSF attached can fry a CPU when it is turned on, but if there is a HSF there then this won't be a problem.
The fact that you aren't getting a POST beep makes me wonder if indeed all connectors are in place, particularly the 4-pin CPU power connector.  Did you mount the mobo using standoffs, or directly to the case?

I have built several computers with the ds3, updating the bios solved the issue with the fan not turning on.

Ah. I dont have a floppy in mine so I cant update my drivers. I did go to the website and update some others, but twice did I get the BSOD for missing files after reboot. Didn't bother troubleshooting, just rebuilt computer.  
 

I have the same board and thought the cpu fan or mb was bad when I installed it. Just like someone said the fan starts as the board does post. If you set the bios for alarms you hear the beep of the cpu fan starting right after power on or reboot. My 6850 runs @ 29-30 degrees @ idle 34-35 under full load. A far cry from my 3.2 prescott which ran at 54-56 with a zalman 9500