Casio Databank 150
If your databank is like mine (DB-35H), there is a TINY spring in a really unusual spot that you probably didn't notice that fell out. Laying the watch face down and with the back off, there is a little tiny hole in the back towards one of the corners. (sorry, already put my watch back together and didn't notice which corner.) There is a tiny (1/16" x 1/4") spring that sits upright in that hole. It must make a contact with the metal cover. I replaced my battery and when I did, a spring fell out. I looked all over the internet, then wrote Casio, who said they didn't have access to the information about where the spring went. (Doh!) I got a used DB-35H from my brother and was going to swap the innards when I noticed the spring on his. Put my spring back and it beeps! If you've lost the spring, don't know if you can fake it with tinfoil or not, but it really is a TINY spring. Good luck.