PC will not stay booted after replacing the motherboard

Dear Gurus,

Need help, it has been awhile since working on pc hardware. I have a Dell 630i pc. The pc started to freeze up after a few minutes. I did not have enough equipment to test all hardward. However I did unplug the hard drive and the pc still locked up while I was in the BIOS. So I took my pc to Geek Squad and they told me the motherboard went bad. Therefore, I called Dell and got a new motherboard. I have replaced the motherboad. Ensured the RAM and cabling is secure. The power led to the motherboard is on. However, when I attempt to turn the pc on, the fans to the video card and processor starts for a split second and the powers down. There is a button on the back of the power supply that if I hold down it will make the fans to continue to run but as soon as I let go of the button the pc powers off again. Also while holding the botton down even though the fans are running the PC does not boot. Any suggestions would be greatly appreciated.

This is my first time posting to this forum.

Thanks,
 
Gurus, please disreagrd this post. I forgot to put to processor in. hehe... I put the fan on but did not put in the processor.
 
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