One can launch Scrivener to open a specific project, in Windows Explorer or My Computer, by navigating to and into the project’s .scriv folder and double clicking (or right clicking, then opening) its .scrivx file (typically named project.scrivx). Likewise, if one can manage to get into Scrivener, one can set Scrivener to not automatically open most recently open project(s) on startup, via Tools > Options > General > unchecking “Reopen projects that were open on quit”.
Let’s assume you have multiple Scrivener projects on your PC, with one being the problematic project and the other being a new test project created from scratch.
If the startup problem occurs when opening the problematic project, but not when opening the other, then the problem is in the problematic project. There are discussions in the forums as to ways to go about dealing with corrupted projects. If this turns out to be what you need and you can’t find such, post back here and I’ll take a stab at locating some.
If the startup problem happens regardless of which project, or no project, is being opened, then the problem is with the installed instance of Scrivener and you need to uninstall, re-download a fresh copy and reinstall Scrivener. Avoid using the updater. Avoid using an already downloaded copy.
NOTE: This will not impact projects, as they are normally stored elsewhere than in the Scrivener program directory. But Scrivener will “forget” where they are (i.e. the newly installed version probably won’t “know”), so be sure to make a note of those locations before uninstalling. Scrivener projects in Windows are folders, having names ending in .scriv. Backups are either folders (names ending in .scriv) or compressed files (names ending in .zip), depending on how you specify backups be done in Tools > Options > Backup. And of course be sure you have off-the-machine backups of any on-the-machine projects, as a general precaution. Once Scrivener is reinstalled, you may have to tell it where projects and backups are/should be.
NOTE: NOTE: You will need to temporarily disable, turn off or uninstall Bitdefender, while doing the uninstall/re-download/reinstall. Before or after this, you may need to go into Bitdefender and exempt Scrivener, as Bitdefender seems to be interpreting something in Scrivener as being a threat (which other such software such as Malwarebytes and Norton Internet Security do not). A search of the forums for “Bitfender” turns up several reports of issues between it and Scrivener. It can presumably be turned back on after all that is done. Malwarebytes and Windows 8 are not a problem. CC Cleaner is probably not a problem. I can’t speak to Superantispyware. The Windows 8 compatibility issue you mention is likely a side effect of issues between Bitdefender and Scrivener during the Scrivener install… i.e. Windows saw Scrivener have startup problems and interpreted that as likely being a compatibility issue).
Hope that helps.