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The app does not start

The app does not start

Nucleus Co-op does not open, closes at once, shows a blank window or complains about a missing file: the runtimes, the antivirus and the folder to check.

On this page

Work through these in order: the first three sections fix almost every case.

Install the runtimes

Nucleus Co-op needs the .NET Framework 4.7.2 or later, the Visual C++ 2015-2022 Redistributable in both x86 and x64, and the Microsoft Edge WebView2 Runtime. Nucleus offers to install the last two on first start; if you declined, install them now, then restart your PC.

On Windows 11, also install the DirectX End-User Runtime if you haven't.

Files go missing

An antivirus that flags some Nucleus Co-op files (input hooks, network emulators) may delete them without asking. An error such as "ProtoInputHooks64.dll is missing from your Nucleus Co-op installation folder" is the classic sign. These detections are false positives.

  1. Add the Nucleus Co-op folder to the Microsoft Defender exclusions, or your antivirus' equivalent.
  2. Extract the release again into that folder, so the missing files come back.

Extract it properly, in the right place

  • Unblock the zip before extracting: right-click, Properties, tick Unblock.
  • Extract with 7-Zip, into a new, empty folder. Don't extract over an older version.
  • Use a folder at the root of a drive, such as C:\NucleusCo-op: not in Program Files, not in OneDrive, your Desktop, Documents or Downloads.

A blank or white window

The interface of Nucleus Co-op 3 is drawn by Microsoft Edge WebView2. If the window opens but stays empty, install or repair the WebView2 Runtime (the Evergreen version), then start Nucleus Co-op again.

Windows blocks it

  • "Windows protected your PC" (SmartScreen): choose More info, then Run anyway.
  • Controlled folder access (ransomware protection in Windows Security) can stop Nucleus Co-op from writing to its folder: allow NucleusCoop.exe in it, or keep the folder out of protected locations.

Still nothing

  • Restart your PC. Leftover game copies or helpers from a crashed session can block a new start.
  • Run it as administrator once: right-click NucleusCoop.exe, Run as administrator. If that works, the folder's permissions are the problem: move Nucleus Co-op to C:\NucleusCo-op.
  • Try a clean copy: extract the latest release into a brand new folder and start it from there.

If it still doesn't open, ask on Discord or report a bug with your Windows version and any error message (a screenshot helps).

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