It's been a few decades but let's keep it simple. Windows can slow over time and if the owner is not a tech oriented person they will reload Windows and it will return to its prior speed. Diagnosing slow Windows has resulted in some hundreds of reasons so without any other clue other than slow, a reload is best.
I have two operating system in my Macbook pro, OS and win7. Now I am using my win7 a lot. Recently, I found the system is getting slow, how can I solve this problem?