Why is it that sometimes my tuner doesnt show what note am i playing - yet is perfectly capable of telling me what is the note of my curses and swears?
What notes are showing and what tuning are you trying to tune to? Some tuners do not show sharp / flat notes. Maybe its set to standard only?

Worst case, your tuner is just breaking down and you need a new one. I personally find tuners from the Apple AppStore (Guitar Toolkit's tuner, to be specific. Though its pretty pricey. UG Tools is good too.) to be very reliable. But it's not a plug in to the guitar king of tuner, so you either have to put it in from of the amp or lying on top of the guitar. Be sure to do that if your tuner isn't the plug in kind.