Check the following in order:

1. A business rule may be set to require Journal Entry approval before a batch shows up to be posted.
a. In General Ledger > Configuration > Business Rules > click Journal Entry 
b. Confirm whether the box is marked for "Journal entry batches must be approved before they can be posted"

If the business rule is marked:
a. In Journal Entry > Open the batch and change the batch status to approved
b. Save and Close the batch
c. Ensure the batch now shows up to be posted

2. Batches that don't have a $0 Balance (equal Debits and Credits) are automatically filtered out through the option in the General Ledger Post window to "only show zero balances".
a. Check the batch balance to ensure the debits and credits match. If they do not, edit the batch.