Operating system is a program that 'tells' and guides the device what to do. If we would compare a computer to human being, the operational system would be like a human psyche. Sometimes it does give troubles and stops operating smoothly: sometimes because of the work overload, sometimes being filled up with useless information or viruses. The best solution is to reinstall the entire system and your computer will be like new. Would be great if you could do the same with our minds, but with constant technology progress who knows-anything can be possible.