Is there a guaranteed hash for every block? Possible Duplicate:
  Nonce size - Will it always be big enough?  




My question may be misphrased, if so, I'll correct it if you let me know in the comments.

My understanding of mining is that the header is appended with some nonce and that is SHA256'd to get some hash, let's say: 7050a40746c695a220acb99c725ef66b29aa863707b17ba939c8bb1f5ec52b67

This happens until there are X number of consecutive 0's in that hash. Is there a guarantee that there will always be at least X 0's in a row for every block header?
There's no guarantee that you can solve a block just by adjusting the nonce.  But there are other things you can change in a block that also change the hash.

This question is pretty much an exact duplicate of your question.