You forgot about the background. The background temp at Earths distance from the sun is around 283K. Room temperature is around 293K, and a computer can operate at 363K. So for an object at 283K the radiation will be (293^4 - 283^4) = , and a computer will be (363^4 - 283^4)
(293^4 - 283^4) = 9.55e8
(363^4 - 283^4) = 1.09e10
So about 10x
I have no problem with your other numbers which I left out as I was just making a very rough estimate.