You need either your wlt file from the old computer and import it into the new computer or use your.private keys to set it up on the new computer. If you dont have either of those then you are out of luck.
If you have XEM at the time of snapshot in your wallet...you will receive an equal amount of XYM. There will be an opt in process built into the wallet when it’s released. You can also buy XYM on exchanges when it’s listed.You will also keep your XEM after XYM is released...XEM will not be burned and continue on as a separate chain.
We don't know what exchanges will be supporting snapshot, though Binance has a good record of support. - However, you should never store your coins on exchange. Remember, "Your keys, your coins. Not your keys, not your coins"Date for snapshot has not been set yet.Get official nem wallet at nem.io/downloads + make a backup of your private key