Q: why is itunes saying it can not locate my music on my computer when i purchased them from itunes. they still work on my phone

If you purchased them, then they should be in the cloud.  Have you tried going to iTunes and there's a way to download purchased content.

Is the media actually on iTunes?

Open Windows Explorer and look for the files in question.

When you find them, if you do, point iTunes to them by selecting the song(s) in question and then when propted select "locate file".

If they are not on the computer, restore them from the backup of the computer or re-download them from iTunes (it does not cost anything to re-download).

Downloading past purchases from iTunes