Re: Does shisha flavour go "off"
And now that I've re-read your post, a year is pretty old especially if it isn't stored in an airtight container. Most flavors can get dry within 6 months or so. And dry shisha makes for harsh smoke and little flavor. There are ways to rewet it, but I'm not exactly sure. Search the forums if you're interested.
Your best bet would be to just buy some new tobacco though.