Take into account, that once you click the "open wallet" on core, it will take a while and might look like the app is frozen. It's just scanning the whole blockchain for transactions on that wallet, and it will most likely take a while, don't panic if that happens (I've seen it happen to a couple of guys).

If you have a moderately big ammount of coins, I'd suggest you buy a hardware wallet to store them, and once the BTCBTC is safe, you can proceed to claim (and dump, or store, that's up to you) the forked coins. IIRC, BCH, BSV and BTG are the ones that are currently worth the effort; you can check how to claim each one of them in LoyceV's guide (and service). But again, securing the BTC should be the top priority