Have you tried to download and reinstall Lightroom?
I have not--I was afraid of what would happen regarding my catalog. I don't want to lose it. It would be the end of the world for a few good photos in progress. But it wouldn't kill me to lose it. But yeah, I have not done that yet because of that. Would I lose my catalog? (That is, if I haven't already "lost" it from my OS crash...)
Re-installing Lightroom will not affect your Catalog you should be able to open it after the install.
The other thing you can try before re-installing Lightroom 5 is to delete your preferences file but it may not make a difference because of the error you are getting.
Look at Preference and other file locations | Lightroom 4 and it will tell you where the lrprefs file is. You can just delete it (if you like rename "Lightroom 5 Preferences.agprefs" to "Lightroom 5 Preferences.agprefs.copy") and try to startLightroom up again.
Update: I uninstalled what I had and reinstalled the newest version. It worked--AND my old catalog got restored! Thanks!