First, let's make sure your poll is Active and Unlocked. You can setermine this two ways:
1) The instructions text says "Respond at..." if it is active, or "When this poll is active, respond..." if the polls is inactive.
2) The Activate Icon is blue instead of grey.
Next, see if you have reached the maximum number of votes allowed per poll. If so, you will need to either clear the results of your poll or purchase a higher vote plan.
If this is an open ended poll, word cloud, or upvote/downvote make sure that the moderation feature is not accidentally enabled.
Make sure you have the proper country's phone number displayed for texting. You can change your text message coverage area by going here: International Text Message Coverage Area
If everything on is clear with those, let's make sure Poll Everywhere is operating normally. Check out status.polleverywhere.com.
If the status is green, please contact Customer Support.