24 pin connectors are usually tight fits.
Check to see that the connector is fully inserted and that it is latched.
Looking at the side, you should see no gap in the line between the connector and the motherboard socket.
Also, check that the individual wires are fully pushed in to the 24 pin connector.
If you ever removed the 24 pin connector by pulling on the cable bundle you may have dislodged some wires.
And... Coolermaster quality is iffy. If this is a new psu, it may be faulty.