I changed my osu skin and it was fine at first, but later most of my songs disappeared even though it gives the actual amount of songs I have in the home screen. When you launch osu. How do I fix this
I really doubt it is skin related. The option to filter beatmaps from 0-10 stars as mentioned by Lyawi is in the middle of the options menu decently close to where you change skins.
It's more than likely that one of the two sliders to control that setting was hit accidentally while scrolling down to change your skin.