Yosemite update problem
Paragon HFS for Windows (or similar) might be your only hope, plus some good disk recovery software on the PC - there is a whole slew of freebies for Windows, but I don't know how good they are. Try http://pcsupport.about.com/od/filerecovery/tp/free-file-recovery-programs.htm The list of available software is constantly changing.

Even if you manage to recover any data, the file names will be gone, so you will then have to dredge through &amp; try to add appropriate names to everything you can recognise.

Then invest in a backup solution &amp; remember the adage
"Any data stored in less than three separate locations ought to be considered temporary.