Maximum # of hashes for finding a block? Since nonce is a 32 bit number, the maximum value of nonce can only be 4,294,967,296. So, if a miner doesn't find the target hash within this number, what happens?
The miner can change the block header hash several different ways:


Change the timestamp. This is the least intrusive, but works just fine. If you can do more than 4 Th/s, this starts to become a problem.
Add transactions. Adding any new transaction changes the Merkle root, so this gives you entirely new nonce spaces.
Change the coinbase transaction. This is the most common method. 32 bits are typically used to act as an additional nonce.