My computer stopped working

I hope someone will be able to help me I've tried all I can think of short of beating my head on the desk.

A few weeks back I did my daily routine of turning on my computer and noticed as I did so that my cpu fan was not wanting to turn so I shut everything down, cleaned out the fan restarted my computer and everything worked fine. The following day I did the same tho the fan would not start at all this time so I turned everything off and changed the fan. After doing this my computer would come on for about 25 - 30 seconds during this time I would see the bios and the prompt to start windows normally or in safe mode. Before being able to click the computer would then shut off and about 5 seconds later power on but not up. I checked to make sure the fan was secure, cleaned the system of all dust and tried again, same result. Finding that the cpu fan was not totally secure I secured it and tried a third time to have the comp do nothing. I get nothing on the monitor nor any power to my keyboard. Since all of this happening I have changed the processor, a new cpu fan, new motherboard, and even a new power supply. Same thing is happening still..
Help please.

I have a gigabyte G41MT-S2PT motherboard
Intel core 2 duo
intel cpu fan
dynex 400 watt power supply
Kingston ddr3
nividia 9500gt
 
I don't have images no but these are the exact items :

Intel Socket 775 Copper Core/Aluminum Heat Sink & 3.5" Fan w/4-Pin Connector up to Core 2 Duo 2.66 GHz

Dynex™ - 400-Watt ATX CPU Power Supply

(purchased at best buy)
 
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