I've just upgraded my store from 1.9.3 (which had a glitch in the search that showed all products when searching) to 184.108.40.206, and now the search shows no products.
What I've tried (and didn't fixed):
When I restore the files from version 1.9.3 the search start "working" again (showing all the products)
The only search module I use is one that show proviews of the products, and this module is working fine.
Some users found problems after the upgrade because a 3rd-party module made an override over Mage_CatalogSearch module.
Can you check if that module is applying a rewrite of some class and cna you test your store without the 3rd-party module?