Well light, for one, is one conversion that energy can make. (Which eventually ends up as heat.. but whatever, I'm talking at the CPU).
1) Light is a form of radiative heat. (Spectroscopy was the topic of the experimental work in my dissertation)
While small, there is some electric energy changed into kinetic (Think electron motion). And then there is the "Things I don't understand but believe exist" possibilities for energy conversion, I'm sure something is going on at the quantum level to disperse energy in a non-heat fashion . All added up, they don't compare to the amount of energy that is converted directly into heat.
2) Now you changed the entire definition of the thermodynamic system involved here.
yes, to be sure, if you partition the system down to just the CPU or even a smaller subset of the micro-world you could argue that some of the energy is temporarily converted into potential energy (capacitance in the system) as well as "work" (kinetic energy)...but you haven't balanced the energy equation until you account for what happens to that potential and kinetic energy as you run out the time-dimension.
At the end of the day if the power meter registers you using 1800W of power then you - all summed up - added 1800W of heat to your surroundings.