I have installed Ubuntu alongside Windows 10 I used the instructions in this answer to How to use manual partitioning during installation?
Firstly I chose something else, secondly made a partition from my hard disk. If I remember correctly, I used Gparted to make a new partition from an empty part of my disk. The installation was successful.
Furthermore, when I boot Windows it works too. I can log into my account in Windows.
However, I get an error message saying
C:\WINDOWS\system32\config\systemprofile\Desktop is unavailable...
Also, I cannot find my data. I cannot even find "this pc" or C drive. Or anything. It seems I've lost my data. But I don't think I deleted it, I think Windows just cannot find the partition.
How can I get my data back?