1. If you search for this address in a block explorer, do you see your balance, or is it empty? Try it: https://live.blockcypher.com/
2. How does your address look like? It starts with a 1, 3 or btc1? And after you import the private key, do they look the same way (starting with 1, 3 or btc1 just like your current wallet) or it's different?
3. Click on Wallet -> Seed, see if your seed is there. If it is, copy it and create a new wallet by restoring it with it. If it's not, try opening your wallet file in a text editor and look for "seed" or "xprv".