Can not add music to library.

I have tried adding music files (MP3) to library and it opens fine and allows me to select it but then it does not appear in the library. I've tried dragging and dropping but nothing. I have also manually added files to the Itunes folder. They appear but not in Itunes. If I uninstall Itunes and reinstall how will this effect the Iphone, and Ipod information apps ect? Will I have to redo all the sign in junk associated? Because honestly with an Iphone and two separate Ipods all with different info and logins is a nightmare I dont want to revisit.