Ok if all of the legs are turned clockwise as far as they will go they are supposed to push into the holes and then lock. If yours won't do that then do this. Turn all of the legs counterclockwise, follow the arrow on top of the leg, as far as they will go. Push the legs into the holes and while holding the leg down turn the leg clockwise as far as it will go. A flat head screw driver works for doing this. Hold down the hsf while you insert the legs into the holes until they are all locked down. If it won't lock into the holes then they might be defective. I personally hate that mounting system as I had trouble with a thermaltake tmg-i1 not locking down but the stock intel hsf did lock down. The enzotech ultra-x I'm using now has a mounting plate so it's much more secure and easier to mount.