Hello Joss

This looks similar to a Windows startup issue we have seen before with Cuelux 1.6.x. Cuelux needs to be able to write files into your Windows Documents folder when starting.
First, please open Command Prompt and run:
echo %USERPROFILE%
If the resulting path contains accented or special characters, please create a new local Windows user with a simple name such as Cuelux, log into that account, install Cuelux 1.6.34 and test again. We are aware of an issue where certain characters in the Windows user-profile path can prevent Cuelux from starting.
Also check whether your Documents folder is managed by OneDrive. We have seen Cuelux fail to start when Documents is redirected or synchronised and Cuelux cannot write its files correctly. As a test, you can temporarily disable OneDrive backup for Documents and also try running Cuelux once as administrator.
If it still does not start, please let us know your Windows version/build from winver, whether Cuelux does nothing at all or briefly opens and closes, and whether your Documents folder is using OneDrive. Cuelux 1.6.34 is currently still the latest Windows release, so there is no need to troubleshoot the CueCable yet; first we need to get Cuelux itself opening correctly.
Hope this helps!