If you can access the bitcoin core without the error try to go to the receiving tab or file>receiving address then copy all addresses.

After that paste all addresses on this tool http://www.homebitcoin.com/easybalance/
Just to check if what addresses have funds.

But if none of them have BTC then it's not worth to dump all of your private keys. But if it shows some address with balances you can export them and just do the guide suggested by BITDV.
If you can't find the console from the BITDV suggestion you can also find it on the windows menu look at the image below.



Then use this command: