If you will go to your last post and click the 'System Specs' in the bottom left of the post, you will find a link to update your system specs. Please fill those out in as much detail as possible, making sure to click save at the bottom of the page. If you would like to know what we would like, you can click 'My System Specs' at the bottom left of this post to see mine. If you do not know what your components are, this will help you accomplish this task. System Specs - Fill in at Ten Forums
When you attempt to start it, do you get anything at all like fans starting, led lights? Are you sure you have the FP Connectors plugged onto the correct pins with the correct polarity? The power button shouldn't make any difference as to polarity. The obvious suggestion would be to make sure all power connectors (24 pin and the 4/8 pin CPU connection)are plugged into the proper connections, and completely seated. Believe it or not, 1/16th of an inch can make a huge difference. If you have a graphics card installed, check those connections also. Are you running a BIOS version of 2100 or above?
Failing all of that, I would disconnect the DVD/CD drive, all hard drives and remove any graphics card you may have installed in the machine, use 1 stick of ram, disconnect all FP wires except the power switch and try to start it. Also, check your manual and see that you have the ram completely seated in the recommended slots. Do you have a Motherboard speaker installed? Are you getting any beeps from it? Any further info you could give us would be helpful in diagnosing it.
Did you install the standoffs in the correct positions making sure there are no extras and ALL standoffs line up with a motherboard hole with no extra standoffs?