You're taking it to the extreme ignoring all real world factors.
Yes, as a thought experiment, the human brain, because it is able to, although extremely inefficiently, perform basic arithmetic and logic operations, could emulate any infinitely complex hardware running any infinitely complex software if all information about the hardware was available and correct and humanly understandable and if the software was available in human readable form and if there was an unlimited means to manually store data and unlimited time to compute and perfect computation accuracy and unlimited ability to focus on said task.
But the converse is true as well I'm afraid. Not only can humans """THEORETICALLY""" emulate computers, but computers can right now in real life accurately emulate a portion of a mammal brain.
By the way, the idea you are describing is called the church-turing thesis. Sure any computational device can theoretically emulate any other, but it's theoretical for a reason. All external factors can not be reproduced. If a computer does calculations based on yesterday's weather, if I don't have yesterday's weather, then those computations can not be emulated.
From the Wikipedia article on Emulation: In a theoretical sense, the Church-Turing thesis implies that any operating environment can be emulated within any other. However, in practice, it can be quite difficult, particularly when the exact behavior of the system to be emulated is not documented and has to be deduced through reverse engineering. It also says nothing about timing constraints; if the emulator does not perform as quickly as the original hardware, the emulated software may run much more slowly than it would have on the original hardware, possibly triggering time interrupts to alter performance.