Make sure that you are synchronizing on the Ethereum blockchain and not on other layers such as BSC or MATIC, and make sure that the wallet is connected to the Internet, the synchronization is correct, and that you clicked on the accounts button and opened accounts.
If this does not work, use
https://iancoleman.io/bip39/ to generate the private key for all your addresses and search for the addresses that have a balance. After you find the balance, insert the private key for that address into the MetaMak wallet, generate a new seed and withdraw all your balance to the new wallet..