Meanwhile, why is Windows 10 so slow? It would be caused by a lot of reasons. In fact, computer running slow has become a common topic for most people and most of them wonder what causes Windows 10 very slow and unresponsive issues and how to fix this issue. Most computer users complain that their computer lags and takes a long time to response or gets stuck with several programs at the same time. Windows 10 Very Slow and Unresponsive FAQ.13 Tips to Windows 10 Very Slow and Unresponsive.