Cydia won't start up on newly jailbroken iPhone 4?

I just jailbroke my iphone 4 with redsn0w and I started up the cydia app and it keeps saying it's "Preparing file system" and that cydia will exit when complete. Eventually it does exit and goes back to my lock screen but when I go to open cydia it does the same thing all over. What should I do?

Try closing Cydia from the app drawer (double click the home button, then press and hold the Cydia app until it jiggles, then tap the red minus sign. Restart the app. If the problem persists, restart your iPhone. And if that doesn't work, your jailbreak might be corrupted, and I suggest you do it over.