Ok a picture of the inside of your computer tower of the way you have it connected up.Also a picture of how the fans are connected.Are you sure it is not the power supply?
Are any fans spinning?Is the
CPU fan spinning?Any lights showing on mainboard or front of tower?
It is either
CPU or
RAM.
I just need a clearer picture of what is happening.
You say you bought a new mainboard did you replace the
CPU?
As the origonal problem may of been
CPU not mainboard.