To engineer a computer to communicate with other computers was an amazing step forward in technology. This technology is not perfect and a number of things can and do go wrong. Today, because of the speed of modems, computers are place under higher stress to process data and deliver this data to your computer screens. Processor speeds are increasing, RAM usage is escalating and hard drives are getting fatter. All due to our ability to obtain data faster and more efficiently.
Computers have to cope with quite a bit.
All this in a few milliseconds. It is therefore important to never assume your computer is operating correctly all the time. The most expensive computers all suffer problems from time to time, they are after all - man made. Therefore if you suspect that your computer is not as healthy as it could be, seek professional assistance. Do not attempt to fix the problem yourself.