Itunes where to put my music for iPod to find

Hey friends,
I know this should be simple, put your music in the "music" file of your PC. plug in the iPod and done, but not what happens. I'll tell you 95% of my songs were not DL'd from iTunes. Everything was fine with my iPod Touch 6th Gen I think, but I got a new PC, moved my songs onto it and now my iPod only holds 91 of my 2,000+ songs. PS I'm more than willing to reset my iPod to factory if it helps.
Guys, I have 10 blown discs and live with pain I pray you never know, so I can't sit at my desk for 3 hours researching this.
Thank you much