If Premiere is acting funny, open Premiere by holding shift+alt and clear the Media Cashe database.
Welcome to the forum.
Between when Titler worked, and now, have you installed any new fonts on your system, or added any programs, that might install fonts (like Open Office)?
Titler is very strict about fonts (more so than PS, InDesign, Illustrator, and others), and if you have installed a corrupt, or just bad font, Titler will often crash, or just not load. It is a min-program, that launches from within PrPro. This ARTICLE goes into a bit more detail.
Try to reset your workspace. It may be that your Titler window is just moved somewhere out of the visible area.
Window > Workspace > Reset Current Workspace