'Entry Point Not Found' Error

[ariehen]

See here:

Error when starting the program

Windows 8.1 is no longer supported by Microsoft, so Electron (the framework Obsidian is built in) has dropped support for it too. I recommend you upgrade to a supported version of Windows (or switch to Linux or another OS) — especially if that computer connects to the Internet.

You can download Obsidian version 1.1.16 here (supported for you), and update to 1.3.3 from within the app (Settings > About screen).