Every breakthrough business idea begins with solving a common problem. The bigger the problem, the bigger the opportunity. I discovered a big one when I took apart an IBM PC. I made two interesting discoveries: The components were all manufactured by other companies, and the system that retailed for $3,000 cost about $600 in parts.
If you think about computing, there isn't just one way to compute, just like there's not just one way to move around. You can have shoes, you can have a car, you can have a bicycle, submarine, rocket, plane, train, glider, whatever. Because you have one doesn't mean you get rid of another one... But PCs continue to be important.