How to recover forgot about Bitcoins
If you withdrew the BTC then you must have had a wallet somewhere to withdraw to. A wallet software could have been installed on your PC or, could be with a web wallet provider or, the balance could still be with your slots.

If you have no information about your wallet (check old emails for account information from a web wallet provider), cannot remember any details and, cannot find any evidence of any Bitcoin wallet on your PC (there are may but, they all make a data folder somewhere..) then, unfortunately, your BTC is lost.