Reinsert the motherboard using the same technique as when removing by angling it a little until the peripheral connectors on the side fit in their holes.

Make sure all connector cables inside the cabinet are on top of the motherboard and not hidden underneath.

Place all the screws in the motherboard, here is where the notes about where the different sizes fit comes in handy.

Connect all the connectors - the sideboard connection, the two small flat cables at the front, the small connector by the harddrive, the ventilator cable.

Attach the keyboard cable. This can be a little tricky but be patient suddenly it will fit in place. There is a small plastic pad that it should fit underneath.