That clears things up for me I think.  I had thought you could just change the nonce until you eventually found the right hash (that's what I meant by checking the same block over and over - changing the nonce and nothing else).  I didn't realize you could go all the way through every possible nonce value and still not find a good hash.  Thanks!

Anybody have an answer to my last question on double hashing?

Hello
2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824 (first round on sha-256)
d7914fe546b684688bb95f4f888a92dfc680603a75f23eb823658031fff766d9 (2nd round of sha-256, from hashing the above value)

However the wiki page above says the 2nd round should yield this value:
9595c9df90075148eb06860365df33584b75bff782a510c6cd4883a419833d50

What am I doing wrong?