When your grandfather updated the PC, did he replace the hard drive, or was it a Windows upgrade?
A Windows upgrade will create a Windows.old folder and in there you may find your content, but don't wait too long. I recommend reading these articles. I hope they help.
It's because of this kind of scenario that we recommend backing stuff up diligently to external drives and to the cloud. As the old saying goes in IT. Programs can be installed easily, but data cannot, so you do your best to guard your data because once it's gone, it's gone forever.