hey does anyone know how to get a new cd key bc i lost mine and im trying to play. please anyone with any info please reply thank you

The only way to get a new legit cd-key is to buy the game again. Often the keys you buy off ebay or any other such sites are not legit. Be very careful about buying keys online because you can't complain to Valve/STEAM about it not working. Only retail keys will give you the right to support.

However you shouldn't need the key if your game is already registered to your steam account. Just log-in to your steam account and you should be fine.