The human brain has a raw computational power of 0.1 quadrillion processes/second. Yes, I said quadrilion. This is, for those who are lazy, basically.... 100,000,000,000,000... half of Bill Gate's bank statement pretty much.
I have a computer sitting in my floor that processes a total of 9,700,000,000 processes per second, and a super computer has roughly two to five thousand processors better than mine. Mine has two dinky ones, comparitivly. So, lets say at the low end this super computer has... two thousand processors, all 200Gb(can buy these as a civilian). (1Gb = 1,000,000,000 processes per second, basically) It is already sitting at 400,000,000,000,000Gb, or processes, per second. Wait a moment, we passed ourselves.
Random thought, as we all know, is not random, it is a mixture of chemicals inside of our brain inwhich fires certain neurons in certain patterns, and voila, randomized thought process. Incidently, this chemical process can be controlled with medication, much like programming.
So yes, if we truly set our minds and pocket books to the task, AI would not be overly difficult, it would be like raising a child. We already have computers that learn on their own, all they lack is that little spark of... well, patterning.
You must remember, we are aware of our surroundings via five senses, without them we'd know nothing and be nothing. Unfortunately, we have yet to figure out how to send data into a computer that replicates a conscious individuals ability to... feel the world. To have emotions, a tightness in your, well processor, when you see something sad, etc. We are learning how to give humans their feelings (such as Touch, Taste, Sight, Hearing and Smell) using machines, its only the next logical step to simply do the same in reverse. Give human sensation to machine, as the individual machines -already- do it on their own.
We ask why we are here because we know we will one day be gone, and unfortunately a computer only knows the time you tell it. We have never attempted to build a computer that, quite litterally, attempted to replicate a human brain as far as function. If we studied a mind for say, a year, we could likely then (As we already have computers that can turn human processes into code) simply allow the computer to learn how the mind reacts to in myriad of stimuli. From this, as we have found with our current 'Learning Computer' technology, they can base other experiences off of previous ones, simply not well. This is because these computers are in small, light, weaponized machines, and in vehicles. Neither of which can handle simply the weight of the processors, let alone the rest of a mainframe.
We have even built Quantum Computers... which litterally, by themselves, blow the figures for human thought out of the water. Thought being meerly variables, and technology advancing at a pace of two times per day... well, it may not be all that long.
DISCLAIMER: THIS DOCUMENT does not cover all individuals in the infinite and variable universe. This is in no way is speaking on cases of incredible, random, or odds of more than 1 : Pi against probability.