With the amount of information provided, my guess is that the CPU cooler isn't making good contact with the CPU. Try to reseat the heatsink and ensure it is fitted tightly to the motherboard.
Not really enough detail here to speculate all that well. What case to what case, all the case fans running, what CPU, etc?
Without any more info given either the fan on the CPU cooler isn't running or you did something to the cooler mount. If you can verify the CPU coolers fan is running I would highly consider remounting the CPU cooler.