Asus M2V - Manual (Page 30)

ASUS M2V 2-9
2. Attach one end of the retention bracket to the retention module base.
3. Align the other end of the retention bracket (near the retention bracket
lock) to the retention module base. A clicking sound denotes that the
retention bracket is in place.
4. Push down the retention bracket lock on the retention mechanism to
secure the heatsink and fan to the module base.
Make sure that the fan and
heatsink assembly perfectly
fits the retention mechanism
module base, otherwise you
cannot snap the retention
bracket in place.