Had the same problem. In my eyes, this is a pretty major bug - while I could not search it turned Evernote from an incredibly useful tool I use everyday to being near useless. Managed to get this back working as well, but instructions above were not clear and took me a while to get working again. Basically needed to type 'Troubleshooting' in the help search box to find it, as was not there by default. Really, there should be a simple click-option to recreate the search indexing around the search box and asking the user if they want to do this immediately after searching, as I can't imagine someone who has used evernote for a long time not wanting to be able to search all their notes.