Hi Joy,
The Resync option will cause FeedBurner to clear out cached content and then fetch and process your feed afresh. That's sometimes useful when FeedBurner's content is stale, but it's not a magical solution to problems with broken feeds, and if your problems have persisted for months, then resyncing alone is unlikely to do you much good.
It's more likely that the content of your source feed is broken somehow. Have you tried using the
W3C Feed Validator on your source feed to check if it's valid?
If you want more specific advice, it helps if you post your FeedBurner URL and the URL of your source feed. It's likely someone will be able to see what's wrong.
- Maks.