Why is My Computer So Slow? The answer is simple. . . you use it. To be brutally honest a computer requires maintenance just like a car or any other appliance that is used frequently and sometimes more so. If your computer is used by multiple people then this becomes especially true. Programs and garbage accumulate and will eventually slow even the fastest computer down to a crawl. In 90% of PC's the culprit lies with malware and useless programs running behind the scenes. Just because you are not using a program doesn't mean it is not running and taking up valuable CPU time and memory resources.