The law of Conservation of Energy says all that input electrical energy going into the system has to be accounted for in the form of some other energy.

Now the only thing moving will be the fans and the hard disks, which means only a very little of that input energy will be converted to kinetic energy.

The system will not be storing energy, meaning none of the input energy is being converted to potential energy.

Now some energy will be lost in the form of noise and light emitted from the leds and monitors etc.

So that only leaves the radiated energy (i.e. the heat) produced by the system.

I would think that heat component would make up the largest portion of that energy pie.