Installing the Motherboard
Ensure that the motherboard mounting area in the computer case is free of obstructions and that all necessary risers have been screwed into the right holes.
If your motherboard came with its own I/O shield, remove the one that came with the computer case - on some cases you need to really bang them out.
Lower the board into the case assuring that the I/O ports on it are correctly aligned with the I/O port shield on the case. Screw the motherboard onto the risers. Some forms of risers will not require screws to be used. You can figure it out.
Consult your motherboard manual for the correct locations of the 'front panel' power and reset button wires, the power and hard-drive LED wires and the speaker. Plug them in.