I went to Genius bar at 南京东路. They helped me to understand what is problem and what I have to do. They also installed OSX to new HDD. Their English is good, so I can communicate without problem. It was big help for me.
I started to use lastpass at this year. If I did not start, re-setup PC would be troublesome.
All my source code is hosted by GitHub, so I can reproduce my development environment onto new HDD.
In my PC, there is a lot of music. The whole size of them is 20GiB. I put them into Dropbox, and it still works after I moved into China. Now I can enjoy to listen my favorite music.