Hello @Artdeck
Sorry you’re having some trouble.
I am assuming you can open other ZBrush files without issue. If you cannot then there is an issue with your installation or hardware environment and you will need to contact Pixologic Support.
If you can open other files then it sounds like this file has become corrupted in some fashion, but I have no explanation from the information provided. Files can fail to open for many reasons, including when they become too large for your system (if your file is approaching 4gb, then you need to worry about this) , if they contain unstable or problematic geometry, or if you are operating ZBrush on hardware that does not meet the recommended specs and there aren’t enough resources for it.
If it is a file size issue, then there may be a few ways you can recover. If you were for some reason saving your Undo History ( I don’t recommend doing this casually for precisely this reason–it rapidly bloats file sizes when there are multiple tools and subtools present), you can try to load it without the Undo History by going to Preferences> Undo History, and enabling “Skip Loading”.
You could also try the “Load Tools from Project” function in the tool menu. If you manage to recover them, immediately save them out as individual tool (.ztl) files. Be aware of the difference between saving a project and a tool file. If all you need to do is save sculpting on a single tool, use the Ztl format to save file size.
If nothing above is useful, you will need to contact Pixologic Support. However, you’re already aware of the most useful solution to your problem:
This is not optional when working with complex graphical software. Until you develop this discipline, you will continue to suffer large setbacks.
Good Luck!