I'd start by figuring out if it is a problem with the database or not. You'll need to figure out where your database lives, then rename the folder. On my vista system, it's users\marc\appdata\local\acd systems\catalogs\pro2\default, or something like that. If ACDSee can start up after renaming the default folder to something else, then the problem is in the db, and the next step would be try restoring from backup or deleting the thumbs files or maybe the cdx files (not sure). If it still doesn't start, though, I'd try reinstalling. And if that doesn't help, looking for recently-installed application that might be causing conflicts.