If you have a Bitcoin QT wallet you need to export your Private Key and Import it into the Bitcoin ABC QT wallet. The Bitcoin ABC QT wallet is currently working - I can see my Bitcoin Cash balance, but no exchanges are accepting deposits yet so you just have to wait.
To export your private key from an Electrum Bitcoin wallet, see the example in the video I did here:
https://youtu.be/XaRWNdRW9kE
To export your private key from a Bitcoin QT wallet as for the OP, you need to go into the console to do it.
Make sure your legacy Bitcoin QT wallet is fully synced. Then go to Help > Debug Window > Console tab, then type these commands to show your private key.
walletpassphrase <yourfullpassword> 6000
dumpprivatekey <yourLegacyBTCaddress>
The walletpassphrase command unlocks your wallet for the number of seconds you provide - here 10 mins in my example, so you can then get your key. The dumpprivatekey command will show your private key that corresponds to your Bitcoin address.
Then to import your private key into your BCH wallet, you need to first download and sync the wallet from BitcoinABC.org. Note, this took me almost 40 hours. Once sync'ed follow the steps as I show in the video and I'll provide text version below:
https://youtu.be/XaRWNdRW9kE
First, as with anything in this space - turn your encryption on under Settings.
Then go to Help > Debug Window > Console tab, then type these commands to Import private key into your Bitcoin ABC wallet.
walletpassphrase <yourfullpassword> 6000
importprivkey <yourBTCprivatekey>
Again, the walletpassphrase command unlocks your wallet for the number of seconds you provide - here 10 mins in my example, so you can then get your key. The importprivkey command will import private key that corresponds to your Bitcoin address. The blockchain will rescan all the transactions for your BTC address and then when it's done you will see your Bitcoin Cash balance in your Bitcoin ABC wallet dashboard.