Do you open Preferences directly to the General tab (Ctrl K) ?
One thing I havee noticed is that going to the Scratch Disks tab can freeze Photoshop for a while if you have a failing hard drive, so I'm wondering what Photoshop looks for and loads when you open Preferences? When you open Photoshop and while the Splash Screen is showing, Photoshop does things like look at what fonts are available, and if just one of those fonts is corrupted it can slow down the start up, or evewn fail to open.
If everything else is OK, then I'd be looking at the Photoshop installation and thinking about reinstalling it. This does depend on your operating system being in good order.