What version of iPad are you using? If you have the iPad3, are you using the built-in dictation - and do you have an Internet connection? If its not the built-in dictation of the iPad3, what app are you trying to use? Lastly, have you tried to fully close out the app you are working in and then try a restart or a reset of the iPad? To do (apologies if you know already):
Fully Close an App: Double tap the Home button (or do a 4-finger swipe up) to reveal a row of icons in the multi-tasking bar. Press and hold an icon until they all start to wiggle and you see a red circle with a minus sign ("-") in the top left. Press the minus sign to fully close the app. Don't worry, it won't remove the app from your iPad, just from the iPad's resident memory.
Then...
Restart: Hold down the power button until the power off slider appears. Slide it off. When the iPad finishes shutting down, hold down the power button again until the Apple logo appears.
If that doesn't help, try this last step...
Reset: Hold both the power and home buttons until the screen goes dark and the Apple logo then appears (the slide to unlock screen may or may not appear). Once the logo appears, release the buttons. After a time, your homescreen will appear. Please note that it may take some time for the Apple logo to appear or for your homescreen to appear (or both). This is normal. Eventually, the homescreen will appear.
Hopefully, that will help. If not, please give us a little more details and we'll see if we can help.
Marilyn