If you are ok with using the commandline, you can use the 'mdls' command to dump the Spotlight data for a file. If there is no Spotlight data, all the dumped fields will start with "kMDItemFS".
You can also use the 'mdutil' command to check if indexing is turned on for that drive.
There's also the privacy tab in Spotlight's preferences. Make sure you double-check that.
Even after all that, sometimes things just get a little wonky and you have to make it re-index. You can use the 'mdutil' command or try following this support article:
http://support.apple.com/kb/HT2409?viewlocale=en_USPost here if you need more help with any of the above.