Friend used recovery software and lost music files + computer now slow

My friend in california had some issues with his computer, so he put a recovery disk his friend gave him thinking it would help him. The recovery disk created a D: drive partition that says recovery, and his computer is much slower to where he cant use it.

He says he should just reinstall windows, that he lost everything already. I told him to wait till I find out more answers.

1) how can we recover lost files that could be in the D: partition
2) what is causing his computer/internet slowdown
3) why did his computer not load windows and asked him to use a recovery disk

thanks