After upgrading to Windows 10, none of the apps you had prior to upgrading are available or listed in Start.
This can happen if, prior to upgrading:
The "Program Files" directory is not located on the system drive.
The "Program Files (x86)" directory is not located on the system drive.
The "ProgramData" directory was relocated from the default location on the "%systemdrive%" drive (the drive that contains the Windows directory).
You will need to go back to your previous version, backup your data, and then reset or re-install Windows and your Apps, so that the “ProgramData” and “Program Files / x86" folders are located on the System drive.
Relocation of the "ProgramData," “Program Files” or "Program Files / x86" directory is not supported in Windows. In order to upgrade to Windows 10 these folder must be on the system drive.
Reset and Restore information:
Redirecting ProgramData or Program Files causes different issues in Windows 8 or 8.1, and redirecting “Users” folders causes other issues in both Windows 10 and 8/8.1 . For more information about that, see Knowledge Base article 2876597.
For more information about the Microsoft policy on relocating the "Users" and "ProgramData" directories, see Knowledge Base article 949977.