have you tried this:/github.com/eagleflies/noblecoin/wiki/Importing-private-keys-from-old-wallet.dat-using---salvagewallet-option
my wallet.dat is encrypted, -salvagewallet is not working for me
Open your old PoW wallet and do "dumprivkey", no need to sync blockchain, then import it to new PoS wallet using "importprivkey" in your wallet console